Warplanes from the US-led coalition targeted two Syrian army positions in the eastern Syrian desert, a military media unit run by Lebanon's Hezbollah group said early on Thursday.
The unit, a Damascus ally, said the strikes took place near T2, an energy installation located near the border with Iraq and about 100km (60 miles) west of the Euphrates River where the coalition is backing ground forces against the Islamic State (IS) group.
A spokesman for the coalition could not be immediately reached by phone.
Eastern Syria was mostly held by IS until last year, when two rival campaigns, one by the Syrian army backed by Russia, Iran and Hezbollah, the other by Kurdish and Arab militias backed by the US coalition, took most of its land.
Communication between Russia and the United States averted most clashes between them. Still, the coalition has struck Syrian pro-government forces that it said were attempting to attack coalition positions.
The US military operating outside the coalition also maintains a base at Tanf in the eastern Syrian desert near the borders with Iraq and Jordan and last year struck pro-government forces moving along a road towards it.
Meanwhile, UN Secretary-General Antonio Guterres has called on Hezbollah not to engage in military activity inside Lebanon and elsewhere in the region, in a report seen by AFP on Wednesday.
"The maintenance by Hezbollah of sizeable and sophisticated military capabilities outside the control of the government of Lebanon remains a matter of grave concern," Guterres said in a report sent to the Security Council on Friday.
The UN chief called on the group "not to engage in any military activity inside or outside Lebanon" in line with a 2004 UN resolution.
The Lebanese government must prevent Hezbollah from "building paramilitary capacity outside the authority of the state," he said.