BEIRUT (Reuters) - An air strike believed to have been carried out by the U.S.-led coalition killed four Syrian military personnel in Deir al Zor province, which is mostly held by Islamic State, a monitoring group said on Monday, in what would be the first time coalition warplanes had hit Syrian government forces.

A source close to the Syrian government confirmed the strike and said there had been casualties and vehicles destroyed.

The Syrian Observatory for Human Rights said the strike hit part of the Saeqa military camp near the town of Ayyash in western Deir al Zor province and wounded 13 military personnel in the first such incident since the coalition began its bombing campaign against Islamic State in Syria.

The strike had hit some time in the last 24 hours, it said.

The U.S.-led force’s campaign is against Islamic State, which controls most of Deir al Zor, including its capital, and has regularly targeted the group in the eastern Syrian province.

In Deir al Zor city, another air strike believed to be carried out by the coalition overnight killed a woman and two of her children, the Observatory said.

Deir al Zor province links Islamic State’s de facto capital in Raqqa with territory controlled by the group in Iraq, and its oilfields are a major source of revenue for the group.