US-led coalition aircraft Thursday struck a pro-regime convoy apparently transporting Shi’ite militiamen in Syria as it headed toward a remote coalition garrison near the Jordanian border, US defense officials said.

While officials stressed the defensive strike did not signal deepening US involvement in Syria’s civil war, it nonetheless raises questions about the ongoing feasibility for the coalition to maintain its singular focus on the Islamic State group.

In a statement, the coalition said the strike had occurred “well inside” an established de-confliction zone northwest of the At-Tanf garrison, where British and US commandos have been training and advising local forces fighting IS.

“A convoy going down the road didn’t respond to numerous ways for it to be warned off from getting too close to coalition forces in At-Tanf,” a US defense official told AFP on condition of anonymity.

“Then there was finally a strike against the lead portion of that movement.”

A convoy of US forces armoured vehicles drives near the village of Yalanli, on the western outskirts of the northern Syrian city of Manbij, on March 5, 2017. (AFP Photo/Delil Souleiman)

A convoy of US forces armoured vehicles drives near the village of Yalanli, on the western outskirts of the northern Syrian city of Manbij, on March 5, 2017. (AFP Photo/Delil Souleiman)

A second defense official told AFP the forces in the convoy appeared to have been a Shi’ite militia.

Attempts to stop the convoy included a call to the Russians — who are working with the Syrian regime — then a “show of force” in the skies above the vehicles, followed by warning shots.

The first official said the convoy was “significant” in size, but only the lead vehicles were hit.

Coalition officials said Russian forces had apparently unsuccessfully tried to dissuade the pro-regime movement south.

Describing the hours-long event as an “escalation-of-force situation,” the official said it did not signal a strategic shift for the coalition, which remains focused on fighting IS group.

Yehya al-Aridi, a spokesman for the Syrian opposition High Negotiations Committee in Geneva, praised the strike.

Smoke rises after strikes from the US-led coalition in the Syrian town of Kobani, on October 10, 2014 (Photo credit: Aris Messinis/AFP)

Smoke rises after strikes from the US-led coalition in the Syrian town of Kobani, on October 10, 2014 (Photo credit: Aris Messinis/AFP)

“We welcome robust action against the foreign forces who have turned Syria into a killing field,” he said.

“Iran and its militias have kept (President Bashar-al) Assad in power. They cannot be allowed to wage war on our soil with impunity.”

America has been militarily involved in Syria since 2014 but has for the most part avoided engaging directly in the country’s civil war.

The biggest exception to this was a US cruise missile attack on a Syrian airbase last month in response to a suspected chemical attack by the regime.

At-Tanf has been the target of repeated attacks in recent months.

Last month, US-led allied forces and Syrian rebels thwarted a significant IS attack on the base.

And in June last year, Russian warplanes bombed the outpost, reportedly just one day after British special forces had pulled out.