Russian warplanes have injured US-back Syrian Democratic Forces (SDF)'s troops, CNN quoted the US-led coalition officials on Sunday.
The strike occurred as both Russian and coalition forces converged on the former ISIS stronghold of Deir Ezzor.
"Russian munitions impacted a location known to the Russians to contain Syrian Democratic Forces and coalition advisers," Operation Inherent Resolve, the US-led coalition, said in a news release.
"Several SDF fighters were wounded and received medical care as a result of the strike."
The strike occurred early Saturday, hitting an area east of the Euphrates River, near the city of Deir Ezzor.
An Operation Inherent Resolve official said that the coalition denied a Russian military request to strike an area in the province of Deir Ezzor, as there were coalition advisers and US-backed Syrian forces there. But the Russians decided to carry out the strike anyway.
The source asked for his name to be withheld because of the sensitivity of the matter.
The extent of the injuries was not clear. No coalition forces were hurt, authorities said.
Both the US-led coalition and Russia are battling ISIS in Syria, but they are on two different sides of the country's civil war.
The US and its allies support some anti-government rebel groups in their fight to overthrow Syrian President Bashar al-Assad. Russia backs his regime.