WASHINGTON — A pro-regime convoy that was struck by US-led warplanes inside Syria this week likely was directed by Iran, US Defense Secretary Jim Mattis said Friday.

The strike on the convoy heading toward a coalition garrison near the Jordanian border was “necessitated by offensive movement with offensive capability of what we believe were Iranian-directed forces,” Mattis said, adding he was not sure if there were Iranians on the ground.

Thursday’s strike occurred inside an established “deconfliction zone” northwest of the At-Tanf garrison, where British and US commandos have been training and advising local forces fighting the Islamic State terror group.

Such zones are agreed upon between Russia and the coalition, and are designed to stop either side inadvertently striking the other’s forces on the ground and in the air.

US forces, accompanied by Kurdish People's Protection Units (YPG) fighters, drive their armored vehicles near the northern Syrian village of Darbasiyah, on the border with Turkey on April 28, 2017. (AFP Photo/Delil Souleiman)

US forces, accompanied by Kurdish People’s Protection Units (YPG) fighters, drive their armored vehicles near the northern Syrian village of Darbasiyah, on the border with Turkey on April 28, 2017. (AFP Photo/Delil Souleiman)

The Pentagon says coalition attempts to stop the convoy from proceeding had included a call to the Russians — who work with the Syrian regime — then a “show of force” in the skies above the vehicles, followed by warning shots.

It appeared the convoy had moved into the area against the advice of the Russians, Mattis said.

“It looks like the Russians tried to dissuade them,” he said.

The Pentagon has stressed the attack did not signal broader US involvement in Syria’s civil war, but Damascus on Friday condemned the strike on pro-government forces as a “brazen attack” and said it would “not be intimidated.”

Russian Foreign Minister Sergey Lavrov looks on during a meeting with his Cypriot counterpart in Nicosia on May 18, 2017. (AFP Photo/Iakovos Hatzistavrou)

Russian Foreign Minister Sergey Lavrov looks on during a meeting with his Cypriot counterpart in Nicosia on May 18, 2017. (AFP Photo/Iakovos Hatzistavrou)

Russian Foreign Minister Sergey Lavrov called the strike a violation of Syrian sovereignty and said he was “unaware” that Russia had been given any warning ahead of the strike.

“We are still confirming the details but according to some reports several dozen civilians died as a result of this strike,” he was reported as saying by Russian news wires.

“It is illegitimate, unlawful and yet another gross violation of Syria’s sovereignty,” Lavrov also said in televised comments while on a trip to Cyprus.

The Russian security council, chaired by Russian President Vladimir Putin, discussed the strike later Friday.

Spokesman Dmitry Peskov, quoted by Russian news agencies, said “it was stressed that such acts are illegitimate and considerably complicate the process of launching de-escalation zones….”

An array of regular and irregular forces are battling alongside the government against rebels, including Russian and Iranian soldiers and militants from Iraq and Lebanon’s Hezbollah group.

Thursday’s strike comes in the context of growing tension over which forces will take on IS in Syria’s east.

President Bashar Assad’s army is trying to prevent US-backed forces from leading that fight.