The United States has shot down a pro-Syrian government drone that opened fire on US-led coalition forces in Syria, a military spokesman said, in a major escalation of tensions between Washington and troops supporting Damascus.

No one was hurt in the incident, which occurred near the coalition’s At-Tanaf garrison, coalition spokesman Colonel Ryan Dillon told Pentagon reporters.

“It was armed and still had weapons on it when it was fired upon by US forces from an aircraft,” Dillon said.

The drone was about the same size as a US MQ-1 Predator. Dillon declined to say who owned or operated the drone, but other officials said it was likely Iranian or Hezbollah.

“It was something that showed a hostile intent, a hostile action and posed a threat to our forces because this drone still had munitions that were still on it,” Dillon said.

At-Tanaf, on the key highway connecting Damascus with Baghdad, has been menaced by a surge of Iran-backed troops loyal to Syrian president Bashar al-Assad.

The area, also just north-east of the Jordanian border, is used by coalition forces as a training and staging area for attacks against Isis.

The coalition has established a “de-confliction” zone, extending 34 miles from the garrison, in which pro-regime and Russian forces are not supposed to operate.

Dillon said the drone had fired on coalition forces patrolling outside the zone.

It was the third such strike in as many weeks, and the second this week, by the Pentagon, which has sought to stay out of Syria’s civil war to focus firepower instead on Isis in Syria and Iraq.

Dillon said the United States had earlier in the day carried out a strike against two pro-Syrian government pickup trucks with weapons that had moved against US-backed fighters near At-Tanaf.

The concern is that such strikes could take away attention from the fight against Isis militants.

“Unfortunately, there have been [these] incidents that have taken our focus away from fighting Isis,” Dillon said, using an acronym for Islamic State.

On Wednesday Kurdish and Arab forces backed by the United States entered Islamic State’s de facto capital of Raqqa, setting the stage for what could be a months-long campaign to reclaim the militants’ largest stronghold in Syria.

For months, air strikes and special forces from the US-led coalition have helped them encircle Raqqa, which Islamic State seized in 2014 and has used as a base to plan attacks abroad.