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                                                                   Exhibit 10.15

                           LIMITED GUARANTEE AGREEMENT

                  LIMITED GUARANTEE AGREEMENT, dated as of October 8, 1999,
(this "AGREEMENT") made by FLAG ATLANTIC HOLDINGS LIMITED ("GUARANTOR"), in
favor of BARCLAYS BANK PLC, as secured party (in such capacity, the "SECURED
PARTY") for the Beneficiaries (as defined below) . Reference is made to the
Credit Agreement, dated as of October 8, 1999 (as the same may be amended,
supplemented or otherwise modified from time to time, the "CREDIT AGREEMENT"),
by and among FLAG Atlantic Limited (the "COMPANY"), the Lenders, Barclays
Capital, as Lead Arranger, WESTDEUTSCHE LANDESBANK GIROZENTRALE, NEW YORK
BRANCH, as syndication agent (in such capacity, the "SYNDICATION AGENT"),
DRESDNER BANK AG, NEW YORK AND GRAND CAYMAN BRANCHES, as documentation agent (in
such capacity, the "DOCUMENTATION AGENT") and Barclays Bank plc, as
Administrative Agent and Security Agent (the Administrative Agent, together with
the Lenders and Lender Counterparties (as herein defined, the "BENEFICIARIES").
Capitalized terms used herein and not defined herein shall have the meaning
ascribed to such terms in the Credit Agreement.

                              W I T N E S S E T H:

                  WHEREAS, pursuant to the Credit Agreement, the Lenders have
severally agreed to make Loans upon the terms and subject to the conditions set
forth therein;

                  WHEREAS, subject to the terms and conditions of the Credit
Agreement, the Company may enter into one or more Interest Rate Agreements
(collectively, the "INTEREST HEDGE AGREEMENTS") with one or more Lenders or
Affiliates thereof (in such capacity, collectively, "LENDER COUNTERPARTIES");

                  WHEREAS, the proceeds of the Loans will be used by the Company
to finance the construction of the Project;

                  WHEREAS, Guarantor directly owns 50% of the issued and
outstanding Capital Stock of the Company, and Guarantor will derive substantial
direct and indirect benefit from the making of the Loans;




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                  WHEREAS, it is a condition precedent to the obligations of the
Lenders to make the Loans that Guarantor shall have executed and delivered this
Guarantee to the Secured Party for the ratable benefit of the Lenders and Lender
Counterparties.

                  NOW, THEREFORE, in consideration of the premises and to induce
the Lenders to make their respective Loans, Guarantor hereby agrees with the
Secured Party, for the ratable benefit of the Beneficiaries, as follows:

SECTION 1.        GUARANTEE

                  1.1. GUARANTEE OF THE OBLIGATIONS. Subject to the provisions
of subsection 1.2, Guarantor hereby irrevocably and unconditionally guarantees
the due and punctual payment in full of all Obligations when the same shall
become due, whether at stated maturity, by acceleration or otherwise pursuant to
the last paragraph of Section 7.1 of the Credit Agreement, (including amounts
that would become due but for the operation of the automatic stay under Section
362(a) of the Bankruptcy Code, 11 U.S.C. Section 362(a) or any similar provision
of any bankruptcy laW); PROVIDED, HOWEVER, that (i) the maximum aggregate amount
of the liability of Guarantor hereunder shall be $100,000,000 (the "GUARANTEED
OBLIGATIONS") and (ii) the Guaranteed Obligations of Guarantor shall be reduced
on a Dollar for Dollar basis by (y) the amount of any equity contribution made
by Guarantor to the Company pursuant to the Equity Contribution Agreement on or
after the date hereof PLUS (z) (1) the amount of any drawing by the
Administrative Agent under Guarantor's Equity Contribution Letter of Credit and
(2) payments by Guarantor under this Guarantee. Such maximum guaranteed amount
in effect from time to time is referred to as the "GUARANTEED AMOUNT."

                  1.2. PAYMENT BY GUARANTOR. Subject to subsection 1.1,
Guarantor hereby agrees, in furtherance of the foregoing and not in limitation
of any other right which any Beneficiary may have at law or in equity against
Guarantor by virtue hereof, that upon the failure of the Company to pay any of
the Obligations when and as the same shall become due by acceleration,
(including amounts that would become due but for the operation of the automatic
stay under Section 362(a) of the Bankruptcy Code, 11 U.S.C. Section 362(a) or
any similar provision of any bankruptcy law), Guarantor will upon demand pay
subject to subsection 1.1, or cause to be paid, in cash, to the Secured Party
for the ratable benefit of the Beneficiaries, an amount equal to the least


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of (i) the Guaranteed Amount and (ii) the sum of the unpaid principal amount of
all Obligations then due as aforesaid, accrued and unpaid interest on such
Obligations (including interest which, but for the filing of a petition in
bankruptcy with respect to Company, would have accrued on such Obligations,
whether or not a claim is allowed against Company for such interest in the
related bankruptcy proceeding) and all other Obligations then owed to
Beneficiaries as aforesaid.

                  1.3. LIABILITY OF GUARANTOR ABSOLUTE. Guarantor agrees that
its obligations hereunder are irrevocable, absolute, independent and
unconditional and shall not be affected by any circumstance which constitutes a
legal or equitable discharge of a guarantor or surety other than payment in full
of the Guaranteed Amount. In furtherance of the foregoing and without limiting
the generality thereof, Guarantor agrees as follows:

                  (a) this Guarantee is a guarantee of payment when due and not
of collectibility;

                  (b) subject to subsection 1.2, the Secured Party may enforce
this Guarantee upon the occurrence of an Event of Default notwithstanding the
existence of any dispute between Company and any Beneficiary with respect to the
existence of such Event of Default;

                  (c) the obligations of Guarantor hereunder are independent of
the obliga tions of Company and the obligations of any other guarantor of the
obligations of Company, and subject as provided in subsections 3.4, 3.5 and 3.6,
a separate action or actions may be brought and prosecuted against Guarantor
whether or not any action is brought against Company or any of such other
guarantors and whether or not Company is joined in any such action or actions;

                  (d) payment by Guarantor of a portion, but not all, of the
Obligations shall in no way limit, affect, modify or abridge any other
guarantor's liability for any portion of the Obligations which has not been
paid. Without limiting the generality of the foregoing, if Secured Party is
awarded a judgment in any suit brought to enforce Guarantor's covenant to pay a
portion of the Obligations, such judgment shall, to the fullest extent permitted
by applicable law, not be deemed to release such Guarantor from its covenant to
pay the portion of the Obligations that is not the subject of such suit, and
such judgment shall, to the fullest extent permitted by applicable law, not,
except to the extent satisfied by such Guarantor, limit, affect, modify or
abridge any other guarantor's liability in respect of the Obligations;



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                  (e) any Beneficiary, upon such terms as it deems appropriate,
without notice or demand and without affecting the validity or enforceability
hereof or giving rise to any reduction, limitation, impairment, discharge or
termination of Guarantor's liability hereunder, from time to time may (i) renew,
extend, accelerate, increase the rate of interest on, or otherwise change the
time, place, manner or terms of payment of the Obligations; (ii) settle,
compromise, release or discharge, or accept or refuse any offer of performance
with respect to, or substitutions for, the Obligations or any agreement relating
thereto and/or subordinate the payment of the same to the payment of any other
obligations; (iii) request and accept other guaranties of the Obligations and
take and hold security for the payment hereof or the Obligations; (iv) subject
as provided in subsections 3.4 and 3.6, release, surrender, exchange,
substitute, compromise, settle, rescind, waive, alter, subordinate or modify,
with or without consideration, any security for payment of the Obligations, any
other guaranties of the Obligations, or any other obligation of any Person with
respect to the Obligations; (v) subject as provided in subsections 3.4 and 3.6,
enforce and apply any security now or hereafter held by or for the benefit of
such Beneficiary in respect hereof or the Obligations and direct the order or
manner of sale thereof, or exercise any other right or remedy that such
Beneficiary may have against any such security, in each case as such Beneficiary
in its discretion may determine consistent herewith or the applicable Interest
Hedge Agreement and any applicable security agreement, including foreclosure on
any such security pursuant to one or more judicial or nonjudicial sales, whether
or not every aspect of any such sale is commercially reasonable, and even though
such action operates to impair or extinguish any right of reimbursement or
subrogation or other right or remedy of Guarantor against Company or any
security for the Obligations; and (vi) exercise any other rights available to it
under the Credit Documents or the Interest Hedge Agree ments; and

                  (f) this Guarantee and the obligations of Guarantor hereunder
shall be valid and enforceable and shall not be subject to any reduction,
limitation, impairment, discharge or termination for any reason (other than a
reduction in the Guaranteed Amount as provided in subsection 1.1 or as a result
of payment in full of the Guaranteed Obligations), including the occurrence of
any of the following, whether or not Guarantor shall have had notice or
knowledge of any of them: (i) subject as provided in subsections 3.4 and 3.6,
any failure or omission to assert or enforce or agreement or election not to
assert or enforce, or the stay or enjoining, by order of court, by operation of
law or otherwise, of the exercise or enforcement of, any claim or demand or any
right, power or remedy (whether arising under the Credit Documents or the
Interest Hedge Agreements, at law, in equity or otherwise) with


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respect to the Obligations or any agreement relating thereto (including, without
limitation, the Equity Contribution Agreement), or with respect to any other
guarantee of or security for the payment of the Obligations; (ii) subject as
provided in subsections 3.4 and 3.6, any rescission, waiver, amendment or
modification of, or any consent to departure from, any of the terms or
provisions (including provisions relating to events of default) of, any of the
other Credit Documents, any of the Interest Hedge Agreements or any agreement or
instrument executed pursuant thereto, or of any other guarantee or security for
the Obligations, in each case whether or not in accordance with the terms hereof
or such Credit Document, such Interest Hedge Agreement or any agreement relating
to such other guarantee or security; (iii) the Obligations, or any agreement
relating thereto (including, without limitation, the Equity Contribution
Agreement), at any time being found to be illegal, invalid or unenforceable in
any respect; (iv) the application of payments received from any source (other
than payments received pursuant to the other Credit Documents or any of the
Interest Hedge Agreements or from the proceeds of any security for the
Obligations, except to the extent such security also serves as collateral for
indebtedness other than the Obligations) to the payment of indebtedness other
than the Obligations, even though any Beneficiary might have elected to apply
such payment to any part or all of the Obligations; (v) any Beneficiary's
consent to the change, reorganization or termination of the corporate structure
or existence of Holdings or any of its Subsidiaries and to any corresponding
restructuring of the Obligations; (vi) any failure to perfect or continue
perfection of a security interest in any collateral which secures any of the
Obligations; (vii) any defenses, set-offs or counterclaims which Company may
allege or assert against any Beneficiary in respect of the Obligations,
including failure of consideration, breach of warranty, payment, statute of
frauds, statute of limitations, accord and satisfaction and usury; and (viii)
any other act or thing or omission, or delay to do any other act or thing, which
may or might in any manner or to any extent vary the risk of Guarantor as an
obligor in respect of the Obligations.

                  1.4. WAIVERS BY GUARANTOR. Except for the rights conferred
under subsection 1.2 and subject to subsections 3.4 and 3.6, Guarantor hereby
waives, for the benefit of Beneficiaries: any right to require any Beneficiary,
as a condition of payment by Guarantor, to proceed against Company, any other
guarantor of the Obligations or any other Person, proceed against or exhaust any
security held from Company, any such other guarantor or any other Person,
proceed against or have resort to any balance of any deposit account or credit
on the books of any Beneficiary in favor of Company or any other Person, or
pursue any other remedy in the power of any Beneficiary whatsoever; any defense
arising by reason of the incapacity, lack


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of authority or any disability or other defense of Company or Guarantor
including any defense based on or arising out of the lack of validity or the
unenforceability of the Obligations or any agreement or instrument relating
thereto (including, without limitation, the Equity Contribution Agreement) or by
reason of the cessation of the liability of Company from any cause other than
payment in full of the Guaranteed Obligations; any defense based upon any
statute or rule of law which provides that the obligation of a surety must be
neither larger in amount nor in other respects more burdensome than that of the
principal; any defense based upon any Beneficiary's errors or omissions in the
administration of the Obligations, except behavior which amounts to bad faith;
any principles or provisions of law, statutory or otherwise, which are or might
be in conflict with the terms hereof and any legal or equitable discharge of
Guarantor's obligations hereunder, the benefit of any statute of limitations
affecting Guarantor's liability hereunder or the enforcement hereof, any rights
to set-offs, recoupments and counter claims, and promptness, diligence and any
requirement that any Beneficiary protect, secure, perfect or insure any security
interest or lien or any property subject thereto; notices, demands,
presentments, protests, notices of protest, notices of dishonor and notices of
any action or inaction, including acceptance hereof, notices of default
hereunder, the Interest Hedge Agreements or any agreement or instrument related
thereto, notices of any renewal, extension or modification of the Obligations or
any agreement related thereto, notices of any extension of credit to Company and
any right to consent to any thereof; and any defenses or benefits that may be
derived from or afforded by law which limit the liability of or exonerate
guarantors or sureties, or which may conflict with the terms hereof.

                  1.5. GUARANTOR'S RIGHTS OF SUBROGATION, CONTRIBUTION, ETC.
Guarantor hereby unconditionally and irrevocably agrees not to exercise any
claim, right or remedy, direct or indirect, that Guarantor now has or may
hereafter have against Company or any of its assets in connection with this
Guarantee or the performance by Guarantor of its obligations hereunder, in each
case whether such claim, right or remedy arises in equity, under contract, by
statute, under common law or otherwise and including without limitation any
right of subrogation, reimbursement or indemnification that Guarantor now has or
may hereafter have against Company with respect to the Obligations, any right to
enforce, or to participate in, any claim, right or remedy that any Beneficiary
now has or may hereafter have against Company, and any benefit of, and any right
to participate in, any collateral or security now or hereafter held by any
Beneficiary unless and until all of the Guaranteed Obligations shall have been
paid in full. Guarantor further agrees that, to the extent the agreement to
withhold the exercise of its rights of subrogation, reimbursement, and
indemnifica-


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tion as set forth herein is found by a court of competent jurisdiction to be
void or voidable for any reason, any rights of subrogation, reimbursement or
indemnification Guarantor may have against Company or against any collateral
or security shall be junior and subordinate to any rights any Beneficiary may
have against Company and to all right, title and interest any Beneficiary may
have in any such collateral or security. If any amount shall be paid to
Guarantor on account of any such subrogation, reimbursement or
indemnification at any time when all Obligations shall not have been paid in
full, such amount shall be held in trust for Secured Party on behalf of
Beneficiaries and shall forthwith be paid over to Secured Party for the
benefit of Beneficiaries to be credited and applied against the Obligations,
whether matured or unmatured, in accordance with the terms hereof.

                  1.6. SUBORDINATION OF OTHER OBLIGATIONS. Any Indebtedness of
Company (other than dividends payable to the Grantor (or any secured party of
the Grantor) as such payment and receipt is provided for in the Shareholders
Pledge Agreement and the Second Priority Security Agreement) now or hereafter
held by Guarantor is hereby subordinated in right of payment to the Obligations,
and any such Indebtedness collected or received by the Guarantor after an Event
of Default has occurred and is continuing shall be held in trust for Secured
Party on behalf of Beneficiaries and shall forthwith be paid over to Secured
Party for the benefit of Benefi ciaries to be credited and applied against the
Obligations but without affecting, impairing or limiting in any manner the
liability of the Guarantor under any other provision hereof.

                  1.7. CONTINUING GUARANTEE. This Guarantee is a continuing
Guarantee and shall remain in effect until all of the Obligations shall have
been paid in full. Guarantor hereby irrevocably waives any right to revoke this
Guarantee as to future transactions giving rise to any Obligations.

                  1.8. AUTHORITY OF GUARANTOR OR COMPANY. It is not necessary
for any Beneficiary to inquire into the capacity or powers of Guarantor or
Company or the officers, directors or any agents acting or purporting to act on
behalf of any of them.

                  1.9. FINANCIAL CONDITION OF COMPANY. Any Loan may be granted
to Company or continued from time to time, and any Interest Hedge Agreement may
be entered into from time to time, in each case without notice to or
authorization from Guarantor regardless of the financial or other condition of
Company at the time of any such grant or continuation or at the time such
Interest Hedge Agreement is entered


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into, as the case may be. No Beneficiary shall have any obligation to disclose
or discuss with Guarantor its assessment, or Guarantor's assessment, of the
financial condition of Company. Guarantor has adequate means to obtain
information from Company on a continuing basis concerning the financial
condition of Company and its ability to perform its obligations under the Credit
Documents and the Interest Hedge Agreements, and Guarantor assumes the
responsibility for being and keeping informed of the financial condition of
Company and of all circumstances bearing upon the risk of nonpayment of the
Obligations. Guarantor hereby waives and relinquishes any duty on the part of
any Beneficiary to disclose any matter, fact or thing relating to the business,
operations or conditions of Company now known or hereafter known by any Benefi-
ciary.

                  1.10.  BANKRUPTCY, ETC.

                   (a) So long as any Obligations remain outstanding, Guarantor
shall not, without the prior written consent of Secured Party acting pursuant to
the instructions of Majority Lenders, commence or join with any other Person in
commencing any bankruptcy, reorganization or insolvency proceedings of or
against Company. The obligations of Guarantor hereunder shall not be reduced,
limited, impaired, discharged, deferred, suspended or terminated by any
proceeding, voluntary or involuntary, involving the bankruptcy, insolvency,
receivership, reorganization, liquidation or arrangement of Company or by any
defense which Company or an Equity Contributor under its Equity Contribution
Agreement may have by reason of any such bankruptcy, insolvency, receivership,
reorganization, liquidation or arrangement proceeding, or by reason of any
order, decree or decision of any court or administrative body resulting from any
such proceeding.

                  (b) Guarantor acknowledges and agrees that any interest on any
portion of the Obligations which accrues after the commencement of any
proceeding referred to in clause (a) above (or, if interest on any portion of
the Obligations ceases to accrue by operation of law by reason of the
commencement of said proceeding, such interest as would have accrued on such
portion of the Obligations if said proceedings had not been commenced) shall be
included in the Obligations because it is the intention of Guarantor and
Beneficiaries that the Obligations which are guarantied by Guarantor pursuant
hereto should be determined without regard to any rule of law or order which may
relieve Company of any portion of such Obligations. Guarantor will permit any
trustee in bankruptcy, receiver, debtor in possession, assignee for the benefit
of creditors or similar person to pay Secured Party, or allow the claim of
Secured Party


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in respect of, any such interest accruing after the date on which such
proceeding is commenced.

                  (c) In the event that all or any portion of the Obligations
are paid by Company, the obligations of Guarantor hereunder shall continue and
remain in full force and effect or be reinstated, as the case may be, in the
event that all or any part of such payment(s) are rescinded or recovered
directly or indirectly from any Beneficiary as a preference, fraudulent transfer
or otherwise, and any such payments which are so rescinded or recovered shall
constitute Obligations for all purposes hereunder.

                  1.11. NOTICE OF EVENTS. As soon as Guarantor obtains knowledge
thereof, Guarantor shall give Secured Party written notice of any condition or
event which has resulted in a material adverse change in the financial condition
of Guarantor or Company or a breach of or noncompliance with any term, condition
or covenant contained herein, any other Credit Document, any Interest Hedge
Agreement or any other document delivered pursuant hereto or thereto.

SECTION 2.        REPRESENTATIONS AND WARRANTIES

                  In order to induce Beneficiaries to accept this Guarantee and
to enter into the Credit Agreement and to make the Loans thereunder, Guarantor
hereby represents and warrants to Beneficiaries that the following statements
are true and correct:

                  2.1. CORPORATE EXISTENCE. Guarantor is a company duly
organized and validly existing under the laws of the jurisdiction of its
organization (and, to the extent applicable in such jurisdiction, is in good
standing under the laws of such jurisdiction) and is duly qualified to do
business in such jurisdiction and in each other jurisdiction in which the
conduct of its business or the ownership or lease of its assets requires such
qualification, except in the case of any such other jurisdiction, where the
failure to be so qualified could not reasonably be expected to have a material
adverse effect on (i) the business, operations, properties, assets, condition
(financial or otherwise) or prospects of Guarantor and its Subsidiaries taken as
a whole; (ii) the ability of any Guarantor to fully and timely perform its
obligations under this Guarantee; (iii) the legality, validity, binding effect
or enforceability against Guarantor of this Guarantee; or (iv) the rights,
remedies and benefits available to, or conferred upon, the Secured Party (a
"MATERIAL ADVERSE EFFECT").


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(a) No filing, recording, publishing or other act is necessary or appropriate in
connection with the establishment of Guarantor except those which have been duly
made or performed and except where the failure to so file, record, publish or
act could not reasonably be expected to have a Material Adverse Effect.

(b) Prior to the Closing Date, Guarantor has not engaged in business other than
that incidental to the development, construction, installation, maintenance and
operation of the Project, the marketing and disposition of Capacity and
activities incidental thereto, and Guarantor has no obligations or liabilities
(contingent or otherwise) other and as previously disclosed to the Agent than
those related to the conduct of such business.

                  2.2. CORPORATE POWER; AUTHORIZATION; ENFORCEABLE OBLIGATIONS.

(a) Guarantor has full corporate power and authority to conduct its business as
now conducted and to execute, deliver and perform this Guarantee.

(b) Guarantor has taken all necessary corporate and legal action to authorize
this Guarantee on the terms and conditions set forth herein and to authorize the
execution, delivery and performance hereof.

(c) This Guarantee has been duly executed and delivered by Guarantor and
constitutes upon execution and delivery thereof by Guarantor, a legal, valid and
binding obligation of Guarantor enforceable against Guarantor, as applicable, in
accordance with its terms, except as enforceability may be limited by applicable
bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium or
similar laws affecting the rights of creditors generally, general principles of
equity (whether considered in a proceeding in equity or law) and an implied
covenant of good faith and fair dealing.

2.3. NO LEGAL BAR TO THIS GUARANTEE. The execution, delivery and performance by
Guarantor of this Guarantee, (i) will not violate or result in a breach of any
Applicable Law, (ii) will not violate or result in a default under any
Contractual Obligation of Guarantor (which violation or default could reasonably
be expected to have a Material Adverse Effect) and (iii) will not result in, or
require, the creation or imposition of any Lien on any of the properties or
revenues of Guarantor, except for Permitted Liens.


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SECTION 3.        MISCELLANEOUS

                  3.1. SURVIVAL OF WARRANTIES. All agreements, representations
and warranties made herein shall survive the execution and delivery of this
Guarantee and the other Transaction Documents and any increase in the
Commitments under the Credit Agreement.

                  3.2. NOTICES.  Any communications between Secured Party and
Guarantor and any notices or requests provided herein to be given may be given
by mailing the same, postage prepaid, or by telex, facsimile transmission or
cable to each such party at its address set forth in the Credit Agreement, on
the signature pages hereof or to such other addresses as each such party may in
writing hereafter indicate. Any notice, request or demand to or upon Secured
Party or Guarantor shall not be effective until received.

                  3.3. SEVERABILITY. In case any provision in or obligation
under this Guarantee shall be invalid, illegal or unenforceable in any
jurisdiction, the validity, legality and enforceability of the remaining
provisions or obligations, or of such provision or obligation in any other
jurisdiction, shall not in any way be affected or impaired thereby.

                  3.4. PARALLEL ACTION. On the date hereof, GTS TransAtlantic
Holdings, the owner of a 50% equity interest in the Company ("GTS Sponsor"), has
entered into a Limited Guarantee Agreement dated the date hereof with provisions
corresponding to the provisions hereof for the Guarantee of the Guaranteed
Obligations by GTS Sponsor. In the event that GTS Sponsor is in default of its
obligations under its Limited Guarantee Agreement and the Guarantor is in
default of its obligations under this Guarantee, then the Administrative Agent
agrees that it will act in parallel to initiate remedies available under the
respective Limited Guarantee Agreements whether such initiative is by demand,
drawing upon the Equity Contribution Letter of Credit (and the corresponding
letter of credit provided by the letter of credit Issuer of GTS Sponsor) or
exercise of remedies of enforcement available pursuant to the respective Limited
Guarantee Agreements. Except as expressly provided for herein, this undertaking
shall in no respect diminish or delay the exercise by the Administrative Agent
of all rights available pursuant to the Guarantor's Equity Contribution Letter
of Credit, the letter of credit provided by the letter of credit Issuer of GTS
Sponsor and the respective Limited Guarantee Agreements. Notwithstanding
anything to the contrary provided for in this Guarantee, in the event that the
exercise of rights by the Administrative Agent under either


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Limited Guarantee Agreement should be delayed, deferred, enjoined or for any
other reason whatsoever the Administrative Agent is unable to exercise in full
or realize in full its rights and obligations under either Limited Guarantee
Agreement, the Administrative Agent may proceed in the exercise of its remedies
under the other Limited Guarantee Agreement to the fullest extent permitted by
law. It is expressly acknowledged by the Administrative Agent that the Limited
Guarantee Agreement entered into by GTS Sponsor has a provision corresponding to
this provision.

                  3.5. CONFIRMATION. It is confirmed by the Company and the
Secured Party that GTS Transatlantic Limited ("GTS SPONSOR") has entered into a
Limited Guarantee Agreement (the "GTS LIMITED GUARANTEE AGREEMENT") on
substantially the same terms as the terms of this Guarantee.

                  3.6. CALLS AND DEMANDS. It is agreed that the Secured Party
will to the extent that equal amounts are due under each such agreements, make
parallel calls and demands under this Guarantee and the GTS Limited Guarantee
Agreement (and if required under any supporting Letters of Credit) at the same
time and for the same amounts and (without prejudice to subsection 3.4) will use
all reasonable endeavors to enforce such calls and demands with a view to
treating the Guarantor and the GTS Sponsor on an equal footing and that, subject
to the provisions of subsections 3.4 and 3.5 of this Guarantee, the initial
amount so demanded or drawn under the Equity Letter of Credit shall be equal to
not more than half of the amount necessary to repay and discharge all
Obligations; provided, however, that such calls and demands shall be made
without prejudice to the obligations of the Guarantor under subsections 1.1 and
1.2 of this Guarantee.

                  3.7. AMENDMENTS AND WAIVERS. No amendment, modification,
termination or waiver of any provision of this Guarantee, and no consent to any
departure by Guarantor therefrom, shall in any event be effective without the
written concurrence of Secured Party and, in the case of any such amendment or
modification, Guarantor. Any such waiver or consent shall be effective only in
the specific instance and for the specific purpose for which it was given.

                  3.8. HEADINGS. Section and subsection headings in this
Guarantee are included herein for convenience of reference only and shall not
constitute a part of this Guarantee for any other purpose or be given any
substantive effect.


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                  3.9. APPLICABLE LAW. THIS GUARANTEE AND THE RIGHTS AND
OBLIGATIONS OF GUARANTOR AND BENEFICIARIES HEREUNDER SHALL BE GOVERNED BY, AND
SHALL BE CONSTRUED AND ENFORCED IN ACCORDANCE WITH, THE INTERNAL LAWS OF THE
STATE OF NEW YORK (INCLUDING WITHOUT LIMITATION SECTION 5-1401 OF THE GENERAL
OBLIGATIONS LAW OF THE STATE OF NEW YORK), WITH OUT REGARD TO CONFLICTS OF LAWS
PRINCIPLES.

                  3.10. SUCCESSORS AND ASSIGNS. This Guarantee is a continuing
Guarantee and shall be binding upon Guarantor and its successors and assigns.
This Guarantee shall inure to the benefit of Beneficiaries and their respective
successors and assigns. Guarantor shall not assign this Guarantee or any of the
rights or obligations of Guarantor hereunder without the prior written consent
of the Majority Lenders. The terms and provisions of this Guarantee shall inure
to the benefit of any transferee or assignee of any Loan transferred or assigned
in accordance with the provisions of the Credit Agreement, and in the event of
such transfer or assignment the rights and privileges herein conferred upon such
Beneficiary shall automatically extend to and be vested in such transferee or
assignee, all subject to the terms and conditions hereof.

                  3.11. CONSENT TO JURISDICTION AND SERVICE OF PROCESS. ALL
JUDICIAL PROCEEDINGS BROUGHT AGAINST GUARANTOR ARISING OUT OF OR RELATING TO
THIS GUARANTEE, OR ANY OBLIGATIONS HEREUNDER, MAY BE BROUGHT IN ANY STATE OR
FEDERAL COURT OF COMPETENT JURISDICTION IN THE STATE, COUNTY AND CITY OF NEW
YORK. BY EXECUTING AND DELIVERING THIS AGREEMENT, GUARANTOR, FOR ITSELF AND IN
CONNECTION WITH ITS PROPER TIES, IRREVOCABLY

                  (a) ACCEPTS GENERALLY AND UNCONDITIONALLY THE NONEXCLUSIVE
JURISDICTION AND VENUE OF SUCH COURTS;

                  (b)  WAIVES ANY DEFENSE OF FORUM NON CONVENIENS;

                  (c) DESIGNATES AND APPOINTS FLAG TELECOM USA LIMITED WITH
OFFICES AT 570 LEXINGTON AVENUE, 38TH FLOOR, NEW YORK, NY 10022, OR SUCH OTHER
PERSONS LOCATED IN NEW YORK STATE AS MAY HEREAFTER BE SELECTED BY THE GUARANTOR
AND AGREEING IN WRITING TO SO SERVE, AS ITS AGENT TO RECEIVE ON ITS BEHALF
SERVICE OF ALL PROCESS IN ANY SUCH PROCEEDINGS


                                       13
<PAGE>

IN ANY SUCH COURT, SUCH SERVICE BEING HEREBY ACKNOWLEDGED BY THE GUARANTOR TO BE
EFFECTIVE AND BINDING SERVICE IN EVERY RESPECT. A COPY OF ANY SUCH PROCESS SO
SERVED SHALL BE MAILED BY REGISTERED MAIL TO THE GUARANTOR AT ITS ADDRESS
PROVIDED IN ACCORDANCE WITH SUBSECTION 3.2 PROVIDED THAT, UNLESS OTHERWISE
PROVIDED BY APPLICABLE LAW, ANY FAILURE TO MAIL SUCH COPY SHALL NOT AFFECT THE
VALIDITY OF SERVICE OF SUCH PROCESS. IF ANY AGENT APPOINTED BY THE GUARANTOR
REFUSES TO ACCEPT SERVICE, THE GUARANTOR HEREBY AGREES THAT SERVICE OF PROCESS
SUFFICIENT FOR PERSONAL JURISDICTION IN ANY ACTION AGAINST THE GUARANTOR IN THE
STATE OF NEW YORK MAY BE MADE BY REGISTERED OR CERTIFIED MAIL, RETURN RECEIPT
REQUESTED, TO THE GUARANTOR AT ITS ADDRESS PROVIDED IN ACCORDANCE WITH
SUBSECTION 3.2, AND THE GUARANTOR HEREBY ACKNOWLEDGES THAT SUCH SERVICE SHALL BE
EFFECTIVE AND BINDING IN EVERY RESPECT. NOTHING HEREIN SHALL AFFECT THE RIGHT TO
SERVE PROCESS IN ANY OTHER MANNER PERMITTED BY LAW OR SHALL LIMIT THE RIGHT TO
BRING PROCEEDINGS AGAINST THE GUARANTOR IN THE COURTS OF ANY OTHER JURISDICTION;
AND

                  (d) AGREES THAT THE PROVISIONS OF THIS SUBSECTION 3.11
RELATING TO JURISDICTION AND VENUE SHALL BE BINDING AND ENFORCEABLE TO THE
FULLEST EXTENT PERMISSIBLE UNDER NEW YORK GENERAL OBLIGATIONS LAW SECTION 5-1402
OR OTHERWISE.

                  3.12. WAIVER OF TRIAL BY JURY. GUARANTOR AND, BY ITS
ACCEPTANCE OF THE BENEFITS HEREOF, EACH BENEFICIARY EACH HEREBY AGREES TO WAIVE,
TO THE EXTENT PERMITTED BY LAW, ITS RESPECTIVE RIGHTS TO A JURY TRIAL OF ANY
CLAIM OR CAUSE OF ACTION BASED UPON OR ARISING OUT OF THIS GUARANTEE. The scope
of this waiver is intended to be all-encompassing of any and all disputes that
may be filed in any court and that relate to the subject matter of this
transaction, including without limitation contract claims, tort claims, breach
of duty claims and all other common law and statutory claims. Guarantor and, by
its acceptance of the benefits hereof, each Beneficiary each (i) acknowledges
that this waiver is a material inducement for Guarantor and Beneficiaries to
enter into a business relationship, that Guarantor and Beneficiaries have
already relied on this waiver in entering into this Guarantee or accepting the
benefits thereof, as the case may be, and that each will


                                       14
<PAGE>

continue to rely on this waiver in their related future dealings with respect to
the transaction contemplated hereby and (ii) further warrants and represents
that each has reviewed this waiver with its legal counsel, and that each
knowingly and voluntarily waives its jury trial rights following consultation
with legal counsel. THIS WAIVER IS IRREVOCABLE, MEANING THAT IT MAY NOT BE
MODIFIED EITHER ORALLY OR IN WRITING (OTHER THAN BY A MUTUAL WRITTEN WAIVER
SPECIFICALLY REFERRING TO THIS SUBSECTION 3.12 AND EXECUTED BY SECURED PARTY
AND GUARANTOR), AND THIS WAIVER SHALL APPLY TO ANY SUBSEQUENT AMENDMENTS,
RENEWALS, SUPPLEMENTS OR MODIFICATIONS TO THIS GUARANTEE. In the event of
litigation, this Guarantee may be filed as a written consent to a trial by the
court.

                  3.13. NO OTHER WRITING. This writing is intended by Guarantor
and Beneficiaries as the final expression of this Guarantee and is also intended
as a complete and exclusive statement of the terms of their agreement with
respect to the matters covered hereby. No course of dealing, course of
performance or trade usage, and no parol evidence of any nature, shall be used
to supplement or modify any terms of this Guarantee. There are no conditions to
the full effectiveness of this Guarantee.

                  3.14. FURTHER ASSURANCES. At any time or from time to time,
upon the request of Secured Party, Guarantor shall execute and deliver such
further documents and do such other acts and things as Secured Party may
reasonably request in order to effect fully the purposes of this Guarantee.

                  3.15. SECURED PARTY AS AGENT.

(a) Secured Party has been appointed to act as Secured Party hereunder by
Lenders. Secured Party shall be obligated, and shall have the right hereunder,
to make demands, to give notices, to exercise or refrain from exercising any
rights, and to take or refrain from taking any action, solely in accordance with
this Guarantee and the Credit Agreement.

(b) Secured Party shall at all times be the same Person that is Administrative
Agent under the Credit Agreement. Written notice of resignation by
Administrative Agent pursuant to Article IX of the Credit Agreement shall also
constitute notice of resignation as Secured Party under this Guarantee; removal
of Administrative Agent pursuant to Article IX of the Credit Agreement shall
also constitute removal as Secured Party under this Guarantee; and appointment
of a successor Administrative Agent pursuant to Article IX of the Credit
Agreement shall also constitute appointment


                                       15
<PAGE>

of a successor Secured Party under this Guarantee. Upon the acceptance of any
appointment as Administrative Agent under Article IX of the Credit Agreement by
a successor Administrative Agent, that successor Administrative Agent shall
thereupon succeed to and become vested with all the rights, powers, privileges
and duties of the retiring or removed Secured Party under this Guarantee, and
the retiring or removed Secured Party under this Guarantee shall promptly (i)
transfer to such successor Secured Party all sums held hereunder, together with
all records and other documents necessary or appropriate in connection with the
performance of the duties of the successor Secured Party under this Guarantee,
and (ii) take such other actions as may be necessary or appropriate in
connection with the assignment to such successor Secured Party of the rights
created hereunder, whereupon such retiring or removed Secured Party shall be
discharged from its duties and obligations under this Guarantee. After any
retiring or removed Secured Party's resignation or removal hereunder as Secured
Party, the provisions of this Guarantee shall inure to its benefit as to any
actions taken or omitted to be taken by it under this Guarantee while it was
Secured Party hereunder.

                  [Remainder of page intentionally left blank]


                                       16
<PAGE>



                  IN WITNESS WHEREOF, each of the undersigned has caused this
Guarantee to be duly executed and delivered by its duly authorized officer as of
the day and year first above written.

                                            FLAG ATLANTIC HOLDINGS LIMITED

                                            By: /s/ Edward McCormack
                                                --------------------------------
                                                  Name: Edward McCormack
                                                  Title:



                                       S-1


<PAGE>



                                            BARCLAYS BANK PLC, as Secured Party

                                            By: /s/ L. Peter Yetman
                                                --------------------------------
                                                  Name: L. Peter Yetman
                                                  Title: Director



                                       S-2