An air strike believed to have been carried out by the US-led coalition killed three Syrian military personnel in Deir al Zor province, which is mostly held by Islamic State, the Syrian Observatory for Human Rights monitoring group said on Monday.
A source close to the Syrian government confirmed the strike and said there had been casualties and vehicles destroyed.
It would be the first time coalition warplanes had hit Syrian government forces.
The Observatory said the strike hit part of the Saeqa military camp near the town of Ayyash in western Deir al Zor province and wounded 14 military personnel in the first such incident since the coalition began its bombing campaign against Islamic State in Syria.
The US-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 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.