A statement from the US -led coalition said the convoy included Syrian forces and militias backed by Iran, and "posed a threat to USA and partner forces", adding that Russian Federation was notified prior to the airstrike.
"The so-called worldwide coalition carried out Thursday an aggression against one of our military points that resulted in a number of martyrs and material damage", an unnamed army official said, according to Syrian state news agency SANA.
The airstrikes came in response to pro-Syrian government forces that posed a threat to USA troops and partner forces near the Jordan border, the coalition said.
US military officials have not yet determined if Syrian army forces were targeted in the strike or if they were militias aligned with the government of Syrian President Bashar Assad.
The Syrian government has said an aerial "aggression" on one of its military positions near the border with Jordan by the US-led coalition killed several soldiers.
"Whatever the reason for the USA strike was, it was illegitimate and marked another flagrant violation of Syria's sovereignty", Russian Foreign Minister Sergey Lavrov said on a trip to Cyprus.
The SANA source added that "those who claim to be fighting [ISIS and al-Qaeda] should direct strikes against them and not against the Syrian Arab Army, which is the only legitimate force that is fighting terrorism along with its allies and friends".
US-led coalition aircraft on Thursday struck a convoy of pro-Syrian regime forces that were "advancing well inside an established de-confliction zone" in southern Syria.
Jubilé pour Lacazette — Lyon-Nice
Marquer les esprits sera donc important, et pour cela vous pouvez comptez sur un Alexandre Lacazette gonflé à bloc. Alexandre Lacazette aura l'occasion de dire adieu à son public, samedi soir contre Nice.
The Syrian military official said the area hit was a military position along the Tanf highway.
A member of the US-backed Syrian rebel forces is cited as saying that the strikes hit a convoy of Syrian and Iranian-backed militias headed toward the At Tanf base.
Defense Secretary Jim Mattis told reporters the US would defend its troops in case of "aggressive" steps against them.
British special forces were first spotted near the heavily fortified Al Tanf base, close to the Jordanian and Iraqi borders, last June.
Yesterday's strike comes in the context of growing tension over which forces will take on IS in Syria's east.
The official was "not sure" which forces were in the convoy but they "were clearly working with the Syrian" regime.
The base at At Tanf has been used by advisers from the US-led global coalition to train "vetted Syrian Opposition" to aid the fight against ISIS. He said: "We are not increasing our role in the Syrian civil war".
In its announcement of the strike, the coalition said it targeted "pro-regime forces". The U.S. -led coalition is also supporting the force with airstrikes.
"The agreed upon deconfliction zone agreement remains in effect", the statement said. The United States in April infuriated the Kremlin by bombing a Syrian regime air base in response to an alleged chemical attack by Damascus.
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