The U.S.-led coalition on Tuesday denied striking Deir al-Zor city in eastern Syria after Damascus accused its jets of killing more than a dozen people.
Syrian state television had said the U.S.-led coalition hit the government-held Qusur district, killing 14 civilians and wounding 32, on Monday.
The British-based Syrian Observatory for Human Rights said it was unclear which aircraft carried out the raid, but that it killed at least 22 people.
Colonel Ryan Dillon, a spokesman for the U.S.-led coalition against Islamic State (IS) militants, said on Tuesday that its jets had not conducted air strikes on any part of the eastern city. The coalition says it investigates any such allegations and is careful to avoid civilian casualties in its bombing runs in Syria and neighbouring Iraq.
The Syrian army controls much of Deir al-Zor city, after pushing into it last month with the help of Russian air strikes and Iran-backed militias. That advance broke an IS siege of an enclave there which had lasted nearly three years.
Syrian troops and allied forces are now fighting IS militants in a few remaining districts of the city, and in nearby parts of Deir al-Zor province.
The U.S.-led coalition has been striking IS targets to back an alliance of Kurdish and Arab militias in other parts of the province across the Euphrates river. The United States and Russia have said they communicate with each other to prevent possible points of conflict between the two separate offensives.