Source: https://ihl-databases.icrc.org/customary-ihl/eng/docs/v1_rul_rule64
Timestamp: 2019-04-26 08:50:27+00:00

Document:
Rule 64. Concluding an agreement to suspend combat with the intention of attacking by surprise the enemy relying on that agreement is prohibited.
State practice establishes this rule as a norm of customary international law applicable in both international and non-international armed conflicts. The rule is based on respect for good faith (see Rule 66). Violations would involve violations of those rules that are implemented via agreements to suspend combat, such as the evacuation of the wounded and sick or civilians (see Rules 109 and 129).
A breach of an agreement to suspend combat constitutes a breach of trust and is a violation of the principle of good faith. The fact that this rule finds its basis in the principle of good faith is expressed in the Lieber Code, which states that “military necessity admits … of such deception as does not involve the breaking of good faith either positively pledged, regarding agreements entered into during the war, or supposed by the modern law of war to exist”. The UK Military Manual emphasizes that “good faith, as expressed in the observance of promises, is essential in war”.
This rule is set forth in numerous military manuals. Some of these manuals consider the feigning of a cease-fire “perfidious”. The US Field Manual and Air Force Pamphlet, for example, state that a false broadcast to the enemy that an armistice has been agreed upon has been widely recognized to be “treacherous”.
The violation of any agreement to suspend combat, whether a truce, armistice, capitulation or other agreement to that effect, is an offence under the legislation of many States. This rule is also supported by official statements, for example, by Iraq in the context of the Iran–Iraq War.
The draft of Additional Protocol II submitted by the ICRC to the Diplomatic Conference leading to the adoption of the Additional Protocols provided that “when carried out in order to commit or resume hostilities … the feigning of a cease-fire” constitutes perfidy. This provision was deleted from the draft during the negotiations in Committee III of the Diplomatic Conference. This does not mean, however, that such acts would be lawful in non-international armed conflicts. The principle of good faith in the implementation of agreements applies equally in international and non-international armed conflicts (see Rule 66).
Military manuals which are applicable in or have been applied in non-international armed conflicts include this prohibition. Violation of the rule in any armed conflict is an offence under the legislation of many States. This rule is also supported by official statements and reported practice in the context of non-international armed conflicts.
No official contrary practice was found. Violations of this rule have generally been condemned. No party to a non-international armed conflict was reported to have claimed the right to conclude an agreement to suspend combat with the intention of attacking by surprise the enemy relying on that agreement.
 Lieber Code, Article 15 (cited in Vol. II, Ch. 18, § 786).
 United Kingdom, Military Manual (ibid., § 803).
 See, e.g., the military manuals of Belgium (ibid., § 787), Burkina Faso (ibid., § 788), Cameroon (ibid., § 789), Canada (ibid., § 790), Congo (ibid., § 791), France (ibid., § 792), Germany (ibid., § 793), Republic of Korea (ibid., § 795), Mali (ibid., § 796), Morocco (ibid., § 797), Netherlands (ibid., § 798), New Zealand (ibid., § 799), Nigeria (ibid., § 800), Senegal (ibid., § 801), Switzerland (ibid., § 802), United Kingdom (ibid., § 803) and United States (ibid., §§ 804–806).
 See the military manuals of Belgium (ibid., § 787), Germany (ibid., § 793), United Kingdom (ibid., § 803) and United States (ibid., §§ 804–805).
 United States, Field Manual (ibid., § 804) and Air Force Pamphlet (ibid., § 805).
 See, e.g., the legislation of Argentina (ibid., §§ 807–808), Azerbaijan (ibid., § 810), Belarus (ibid., § 811), Bolivia (ibid., § 812), Chile (ibid., § 813), Costa Rica (ibid., § 814), Ecuador (ibid., §§ 815–816), El Salvador (ibid., § 817), Ethiopia (ibid., § 818), Guatemala (ibid., § 819), Hungary (ibid., § 820), Italy (ibid., §§ 821–822), Mexico (ibid., § 823), Netherlands (ibid., § 824), Nicaragua (ibid., § 825), Peru (ibid., §§ 826–827), Spain (ibid., §§ 828–829), Switzerland (ibid., § 830) and Venezuela (ibid., §§ 831–832); see also the draft legislation of Argentina (ibid., § 809).
 Iraq, Letter to the UN Secretary-General (ibid., § 835) and Military communiqué of 1 March 1987 (ibid., § 836).
 Draft Additional Protocol II, Article 21(1) (ibid., § 785).
 See, e.g., Germany, Military Manual (ibid., § 793).
 See, e.g., the legislation of Azerbaijan (ibid., § 810), Belarus (ibid., § 811), Costa Rica (ibid., § 814), Ecuador (ibid., § 815), El Salvador (ibid., § 817), Ethiopia (ibid., § 818), Nicaragua (ibid., § 825), Spain (ibid., § 829), Switzerland (ibid., § 830) and Venezuela (ibid., § 831); see also the legislation of Argentina (ibid., § 808), Hungary (ibid., § 820) and Italy (ibid., §§ 821–822), the application of which is not excluded in time of non-international armed conflict, and the draft legislation of Argentina (ibid., § 809).
 See, e.g., the statements of China (ibid., § 834) and Yugoslavia (ibid., § 837) and the reported practice of Yugoslavia (ibid., § 839) and a State (ibid., § 840).

References: § 786
 § 803
 § 787
 § 788
 § 789
 § 790
 § 791
 § 792
 § 793
 § 795
 § 796
 § 797
 § 798
 § 799
 § 800
 § 801
 § 802
 § 803
 § 787
 § 793
 § 803
 § 804
 § 805
 § 810
 § 811
 § 812
 § 813
 § 814
 § 817
 § 818
 § 819
 § 820
 § 823
 § 824
 § 825
 § 830
 § 809
 § 835
 § 836
 § 785
 § 793
 § 810
 § 811
 § 814
 § 815
 § 817
 § 818
 § 825
 § 829
 § 830
 § 831
 § 808
 § 820
 § 809
 § 834
 § 837
 § 839
 § 840