BEIRUT -- The U.S. sent aircraft to strike Syrian regime vehicles on Thursday that violated a deconfliction zone set up around al-Tanf, an army base where special forces are training Syrian militias, CBS News national security correspondent David Martin reports.

American officials and Syrian activists said the strike hit the pro-Syrian government forces as they were setting up fighting positions in a protected area in the desert near the border with Jordan. A bulldozer and a tank were hit, although it was unclear if it struck the Syrian army or just militias allied with the government.

The region around al-Tanf, where the borders of Jordan, Syria and Iraq meet, has been considered a deconfliction zone, under an agreement between the U.S. and Russia.

The Syrian regime has violated the zone two times in the past few days, Martin reports.

In one incident, 27 regime vehicles drove within 18 miles of al-Tanf, which breached the 34 mile radius of the army convoy. U.S. aircraft attempted to buzz the regime, but when the convoy didn't turn around, they conducted a strike against some of the vehicles.

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In the second incident, an unarmed Syrian SU-22 fighter-bomber entered the deconfliction zone and was intercepted by a pair of F-22 fighter aircraft.

Speaking to reporters, Defense Secretary Jim Mattis said the U.S. will defend its troops in case of "aggressive" steps against them. He was asked if the airstrike increases the U.S. role in the Syrian war.

"We are not increasing our role in the Syrian civil war, but we will defend our troops," Mattis said. "And that is a coalition element made up of more than just U.S. troops, and so we will defend ourselves (if) people take aggressive steps against us."

The U.S. strike marks a new approach in what has become an intensely crowded and complicated war zone. Thursday's strike was the coalition's first on pro-Assad forces in the battlefield. The coalition had so far kept its military operations focused on Islamic State militants and al-Qaida-linked groups.

Operation Inherent Resolve, the U.S.-led campaign against the Islamic State of Iraq and Syria (ISIS), said in a statement that "the coalition struck pro-regime forces that were advancing well inside an established de-confliction zone" and "posed a threat to U.S. and partner forces" at al-Tanf.

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It said the action was taken after "apparent Russian attempts to dissuade Syrian pro-regime movement" toward al-Tanf were unsuccessful, and after a "coalition aircraft show of force" and warning shots.

"The agreed upon de-confliction zone agreement remains in effect," the statement said.

It remains unclear why the Syrians violated the zone. Martin reports that Syrian forces are pushing eastward toward the Euphrates River Valley, which hints to the idea that the regime may have been doing reconnaissance on their flank.

The base was attacked by ISIS in April. Last summer, Syrian fighters trained by the U.S. who operated out of al-Tanf were bombed by Russian jets.

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ISIS attacks Syrian state-held areas

ISIS attacked several government-held villages in central Syria on Thursday, capturing at least one of them in violence that left 52 people dead, including 11 women and 17 children.

Some of the women were beheaded and others had their limbs amputated. Children's bodies were mostly dismembered due to the fact they were beaten with heavy objects such as bricks or stones. Most of the men died from shelling or heavy machine gun fire.

Hospital officials say 120 people were wounded in the attack.

The attack in the central Hama province targeted villages where most residents belong to the Ismaili branch of Shiite Islam, raising fears the extremists might massacre them, as they have in other minority communities in Syria and Iraq.

The villages are located near the town of Salamiyeh and the highway that links the capital, Damascus, to the northern city of Aleppo, but state media said traffic was not affected.

The attacks come as goverment forces are on the offensive against the extremists in other parts of Syria, mostly in the northern province of Aleppo and the central Homs region and to the east.

U.S.-backed and Kurdish-led forces are meanwhile marching toward the extremists' de-facto capital of Raqqa, in northern Syria. </s> U.S.-led coalition jets reportedly struck Syrian and allied forces inside Syria. BuzzFeed News cited a U.S. defense official as confirming the strike was launched by the U.S. That would mark the first time the Syrian regime has been directly targeted by the U.S. since President Trump ordered a missile strike last month in response to the Assad regime’s use of chemical weapons—and they also mark an escalation in the U.S. involvement in the Syrian civil war.

BuzzFeed added the strikes occurred near al-Tanf, near Syria’s border with Jordan and Iraq, where U.S. and U.K. special-operations forces train Syrian rebels.

CBS News reported that the strikes were in response to Syrian regime vehicles violating a deconfliction zone set up around the military base in al-Tanf. It said Assad’s regime had violated the zone twice in recent days. Here’s more:

In one incident, 27 regime vehicles drove within 18 miles of al-Tanf, which breached the 34 mile radius of the army convoy. U.S. aircraft attempted to buzz the regime, but when the convoy didn't turn around, they conducted a strike against some of the vehicles. In the second incident, an unarmed Syrian SU-22 fighter-bomber entered the deconfliction zone and was intercepted by a pair of F-22 fighter aircraft.

Fars, the Iranian news agency that is allied with Iran’s Islamic Revolutionary Guard Corps, reported that 3,000 fighters from Hezbollah, the Iran-backed Lebanese Shia militia, were deployed to Tanf “to prepare the Syrian army and its allies for thwarting the U.S. plots in the region and establish security at the Palmyra-Baghdad road.” It said the Syrian military and others had also been sent to the region. </s> The U.S. bombed a convoy of pro-Assad fighters Thursday as they advanced on U.S. “partner forces,” according to the coalition’s official Twitter account.

Another tweet added that the strike came only after several attempts to warn the convoy from advancing any further.

The al-Tanf area referenced is home to a base where U.S. special forces train anti-ISIS fighters. It’s surrounded by a deconfliction zone. The pro-Assad forces got too close to that zone, USA Today reports, adding that the “airstrike targeted a tank and two earth movers that were building fighting positions within the defensive zone.”

U.S. military is not yet certain if those bombed were Syrian army or pro-Assad militia, USA Today notes. BuzzFeed says the convoy included “regime-allied militia mixed with Syrian government forces.” And a leader from a “Pentagon-backed rebel group” told Reuters that the forces were made up of the “Syrian army and Iranians.”

A strike on pro-Assad forces, be they militia troops or members of the Syrian army, marks a turn from the reason the U.S. is in Syria — to fight ISIS. This is only the second time the U.S. has bombed pro-Assad targets after last month’s strikes on an airfield in retaliation for a chemical attack.

Fighting Assad and ISIS at the same time is not only “madness and idiocy,” as Trump said last year, it’s potentially illegal given the lack of Congressional authorization to strike regime targets. That’s a point one Democratic lawmaker is already making. </s> The coalition strikes occurred near At Tanf town, where US' and British special operations forces have been training Syrian rebel fighters near the border with Iraq and Jordan.

"The coalition struck pro-regime forces… after apparent Russian attempts to dissuade Syrian pro-regime movement south towards At Tanf were unsuccessful, a coalition aircraft show of force and the firing of warning shots," the statement said.

The deconfliction memprandum on flights over Syria set up between the United States and Russian military remains in focre despite the US-led coalition's strike on Syrian government troops, the coalition added.

"The agreed upon de-confliction zone agreement remains in effect," the statement said.

The United States and Russia signed the bilateral memorandum of understanding in October 2015 to ensure their flight safety during combat missions over Syria.

On Monday, Al-Masdr News reported that Syrian Arab Army soldiers along and militias affiliated with the Iraqi Popular Mobilization Units are preparing to recapture the nearby Tanf Border crossing from Daesh. </s> American warplanes have attacked pro-Assad forces for the first time to protect a base used by British special forces and other allies on a covert mission in Syria.

US Air Force jets fired at troops advancing on a ‘de-confliction zone’ near Al Tanf, where elite UK soldiers on a training mission are based.

The US had already agreed with Russia, which backs Syrian dictator Bashar al-Assad, that there would be no fighting in the area around Al Tanf.

But the pro-Assad convoy of 20 vehicles was deemed to ‘pose a threat to US partner forces’, and continued to advance across the desert following Russian attempts to stop it.

The airstrikes on Thursday mark the first time the US military has deliberately hit pro-government forces in response to a threat against Western troops.

The attack, which was condemned by Syria and Russia and which threatens to inflame the war, came as President Trump set off on his first international trip to the Middle East.

British special forces were first spotted near the heavily fortified Al Tanf base, close to the Jordanian and Iraqi borders, last June.

They are gathering intelligence, including the location of British foreign fighters for the RAF to kill, as well as training moderate Syrian rebels. Syria slammed the airstrike as a ‘blatant attack on forces fighting terrorism’ and said several people were killed. Syrian government negotiator Bashar al-Ja’afari said he had raised the ‘massacre’ committed by the US ‘aggressor’ with the UN.

Russia’s deputy foreign minister Gennady Gatilov said the destruction of the convoy was a ‘breach of Syrian sovereignty’ and an attack against Syrian armed forces was ‘completely unacceptable’.

The convoy, which included four tanks, was 17 miles from Al Tanf when it was struck.

A US-led coalition commander attempted to get the pro-Assad forces out of the zone by dispatching two US aircraft as ‘a show of force’. The jets then fired warning shots to get the vehicles to turn back, Pentagon officials said.

When the forces did not respond, but began setting up fighting positions in the protected area, they were attacked.

A member of US-backed rebel forces said the convoy included Syrian and Iranian-backed militias heading towards Al Tanf when it clashed with rebel forces.

The strike was a defensive move to protect allies, US officials said.

Defence secretary James Mattis denied the attack marked an escalation of America’s role in Syria. He said: ‘We are not increasing our role in the Syrian civil war. But we will defend our troops.’

The Ministry of Defence said the RAF did not take part in the strikes. MPs have not given approval for the RAF to strike any targets in the country except those belonging to IS. </s> Earlier in the day, BuzzFeed News reported that a US-led coalition spokesperson has confirmed that coalition strikes in southern Syria struck Syrian government armed forces.

The coalition strikes reportedly occurred near At Tanf town, where US’ and British special operations forces have been training Syrian rebel fighters near the border with Iraq and Jordan.

“The strike did happen. It was against a pro-regime force operating in the vicinity of At Tanf. This regime force was operating within a well-established de-confliction zone,” the defense official told Sputnik.

The US defense official added that the US coalition commander considered the pro-Assad forces as a threat to coalition troops.

“The commander on the ground perceived this force to be a threat to coalition forces,” the defense official said.

It is unclear yet whether the strikes have killed any soldiers or pro-government militia fighters as there has been no official comment from Damascus so far.

The US-led coalition said that the agreement on a de-confliction zone with Russia remains in effect despite the strike on Syrian army.

The United States and Russia signed the bilateral memorandum of understanding in October 2015 to ensure their flight safety during combat missions over Syria.

On Monday, Al-Masdr News reported that Syrian Arab Army soldiers along and militias affiliated with the Iraqi Popular Mobilization Units are preparing to recapture the nearby Tanf Border crossing from Daesh.

Media reports suggested that Syrian rebels have voiced concerns over the Syrian army getting “too close” to the US Special Forces’ base in At Tanf.

In April, Daesh terrorists attempted to take the US base near At Tanf in which three US-backed Syrian rebels were killed.

This was not the first time the US-led coalition intentionally or accidentally struck the Syrian army fighting against Daesh. In the early hours of April 7, the United States launched 59 Tomahawk cruise missiles at the Syrian military airfield in Ash Sha’irat, located about 40 kilometers from the city of Homs. Moreover, on September 17, 2016, US-led coalition aircraft carried out four strikes against the Syrian army near the Deir ez-Zor airport, killing 62 soldiers and wounding some 100. </s> Pro-Syrian government forces hit by U.S.-led coalition airstrikes in an established deconfliction zone inside Syria were directed by Iran, U.S. Secretary of Defense Jim Mattis said Friday.

Mattis told reporters at the Pentagon the strikes were conducted in "self-defense" and were "necessitated by offensive movement with offensive capability of what we believe were Iranian-directed forces." He added that it was unclear whether Iranians were on the ground with the forces.

U.S. Central Command spokesman Major Josh Jacques said in an interview with VOA on Thursday that pro-Syrian government forces set up a convoy northwest of the al-Tanf army base — where U.S.-led coalition forces are training Syrian militias fighting Islamic State — with Syrian tanks, bulldozers, armored vehicles, artillery vehicles and technical vehicles, and began creating fighting positions for their tanks.

Coalition strikes destroyed one of the tanks, two front-end loaders, another piece of construction equipment and a tactical vehicle, according to a U.S. Central Command strike release.

Officials say some of the pro-Syrian government forces are still violating the deconfliction zone set up around the al-Tanf base. The zone has been established as the area within a 55-kilometer radius from the base.

"We're calling on them to withdraw from the deconfliction zone," Jacques told VOA.

Over several hours, the coalition flew aircraft through the airspace and fired missiles into the ground as "warning shots" near the pro-Syrian forces, but they continued building their positions, Jacques said.

The coalition also used a deconfliction hotline established between the U.S. and Russia to see if the Russians could get them to leave the area, but several apparent Russian attempts led to no change from the forces.

"It looks like the Russians tried to dissuade them," Mattis said Friday.

"After that, we couldn't do much else," Jacques said. "They had every opportunity to leave the area."

Syria has condemned the deadly coalition attack and said airstrikes near the border with Jordan are hampering efforts by the Syrian army and its allies to fight Islamic State.

Syrian rebels hailed the coalition raids and encouraged further actions against the pro-Syrian government forces and Shi'ite militias who also are trying to gain control of the strategic border point.

"What happened today demonstrates that they cannot reach our territories," Al-Baraa Fares, a spokesman for the rebel group Maghaweer Al Thawra, told VOA. "When they tried, we informed the collation airplanes, which destroyed their convoys."

A U.S. official estimated that "possibly dozens of fighters" convoyed into the restricted area ahead of the airstrike. Another official put the number of pro-government fighters inside the deconfliction zone at a "couple hundred."

"The strike was not a change in policy," but rather an instance of the commander on the ground calling for force protection, according to a third official.

A statement from the coalition Thursday confirmed the deconfliction zone agreement remains in effect.

Jacques also said that Russia had agreed to call the United States to deconflict whenever they planned to operate in the area within 55 kilometers of the base. The Russians had used the hotline less than 24 hours before the Syrians violated the space.

"The line's been up and running," he noted.

The U.S. military says it does not communicate with pro-Syrian government forces and speaks with Russian forces only when needed to prevent miscalculations, since U.S. and Russian aircraft both conduct bombing missions in Syrian skies.

"We will never work with the Assad regime," Brett McGurk, the special presidential envoy for the counter-IS coalition, told Pentagon reporters Friday.

Anti-IS coalition forces have been operating in the al-Tanf area for many months. Their focus has been to train and advise Syrian rebel groups on how best to capture key terrorist-controlled territories on the Syrian southern border with Jordan and Iraq.

The pro-Syrian government forces were 25 kilometers away from al-Tanf base when they were targeted by coalition planes, according to Fares.

Fares said the pro-Syrian government forces tried but failed to receive reinforcement from nearby Shi'ite militias.

Ahed Al Hendi from the VOA Extremism Watch Desk contributed to this report. </s> The coalition strikes reportedly occurred near At Tanf town, where US' and British special operations forces have been training Syrian rebel fighters near the border with Iraq and Jordan.

"The strike did happen. It was against a pro-regime force operating in the vicinity of At Tanf. This regime force was operating within a well-established de-confliction zone," the defense official told Sputnik.

The US defense official added that the US coalition commander considered the Syrian army as a threat to coalition troops.

"The commander on the ground perceived this force to be a threat to coalition forces," the defense official said.

On May 4, Russia, Turkey and Iran signed a memorandum on the establishment of safe zones in war-torn Syria as part of the the Astana talks on Syrian settlement. The four zones include the northwestern Idlib province and parts of the neighboring Latakia, Hama and Aleppo provinces, the north of the central Homs province, eastern Ghouta near Damascus and certain parts in the country's southern Deraa and Quneitra provinces. The memorandum on these de-escalation zones took effect on May 6.

On Monday, Al-Masdr News reported that Syrian Arab Army soldiers along and militias affiliated with the Iraqi Popular Mobilization Units are preparing to recapture the nearby Tanf Border crossing from Daesh.

In April, Daesh terrorists attempted to take the US base near At Tanf in which three US-backed Syrian rebels were killed.

This was not the first time the US-led coalition intentionally or accidentally struck the Syrian army fighting against Daesh. In the early hours of April 7, the United States launched 59 Tomahawk cruise missiles at the Syrian military airfield in Ash Sha’irat, located about 40 kilometers from the city of Homs. Moreover, on September 17, 2016, US-led coalition aircraft carried out four strikes against the Syrian army near the Deir ez-Zor airport, killing 62 soldiers and wounding some 100. </s> In this image provided by the U.S. Air Force, an F-16 Fighting Falcon takes off from Incirlik Air Base, Turkey, as the U.S. on Wednesday, Aug. 12, 2015, launched its first airstrikes by Turkey-based F-16 fighter jets against Islamic State targets in Syria, marking a limited escalation of a yearlong air campaign that critics have called excessively cautious. (Krystal Ardrey/U.S. Air Force via AP))

The US military launched airstrikes against pro-Assad forces in southern Syria on Thursday, three US defense officials confirmed to BuzzFeed News.

It marked the second time under the Trump administration that the US has struck out against President Bashar al-Assad’s forces with airstrikes and first in the apparent vicinity of US troops operating inside Syria.

BuzzFeed News is the first to have reported US confirmation that it launched these new strikes.

The strikes were believed to have hit a regime-allied militia mixed with Syrian government forces, US officials said. They hit advancing vehicles outside a base called Tanf, near the Jordanian border. As BuzzFeed News reported last week, US Special Forces are deployed at the base with a unit of Syrian rebels. The Special Forces are training the rebels to fight ISIS — and also accompanying them on combat missions against the militants.

But the Syrian regime and its allies — including Iranian forces, Shiite militia, and Hezbollah — are also based some 40 miles outside Tanf, a rebel commander based there told BuzzFeed News last week, allowing them easy access to Tanf via a highway that cuts through the desert.

Unlike the US strike against the al-Shayrat air base in March, which the Trump administration ordered in retaliation for a regime chemical weapons attack, Thursday’s strike seemed designed to protect the US forces based at Tanf.

One of the defense officials — who, like the others, spoke on condition of anonymity to reveal details that the Pentagon had yet to make public — said that the US acted to stop an advance of pro-regime forces toward Tanf. Pro-regime forces had crossed a pre-agreed deconfliction zone and continued to advance despite warning strikes, he added. The strikes destroyed several vehicles. It was unclear if they resulted in any deaths.

The 5th Special Forces Group has been training and mentoring pro-Western rebel groups in and around Tanf for about six months as part of the anti-ISIS campaign developed under then-President Barack Obama and continued by the Trump administration.

While contact with ISIS units is to be expected considering the mission, this is the first instance of American air power being used against pro-Assad forces to support American troops and their rebel allies.

With a mission that focuses completely on ISIS, US troops have rarely had to worry about operating in close proximity to Syrian forces and their aligned militias. The last encounter between the groups occurred last month when Syrian troops passed near a special operations group in the Kurdish areas, but that remained peaceful. As the territory dominated by ISIS collapses in the face of advances by Kurdish forces in Syria and Iraq forces in Mosul, though, the world’s most crowded battlespace further shrinks.

While the Trump administration has been firm in its opposition to ISIS, its policy towards the Assad regime has shifted rapidly at times. Prior to the chemical attack in April, Secretary of State Rex Tillerson and others indicated that Assad may remain in power as part of a deal to end the ongoing civil war. Since then, Tillerson and Trump have called for Assad’s exit.

With additional reporting by Mitch Prothero in Brussels.
United States aircraft bomb a convoy belonging to the Syrian pro-government militia within a so-called "deconfliction zone" around Al-Tanf.