One man was killed when US troops in north-east Syria returned fire after their convoy came under attack near a checkpoint manned by forces loyal to Bashar al-Assad on Wednesday.
At one point in the standoff, a Russian army convoy also arrived at the scene in an apparent attempt to mediate the rare confrontation involving US and Syrian fighters.
A Pentagon spokesman said US-led coalition forces were conducting a patrol near the town of Qamishli when they encountered a checkpoint occupied by pro-government forces.
“After coalition troops issued a series of warnings and de-escalation attempts, the patrol came under small arms fire from unknown individuals,” said Col Myles Caggins, a spokesman for the US-led coalition.
“In self-defense, coalition troops returned fire,” he said.