The Russian and US governments have blamed each other for a collision between Russian and US armoured vehicles in north-eastern Syria in which several US troops were injured.
Video of the collision was broadcast by a Russian nationalist website, Rusvesna.su, then widely retweeted.
The video appears to show a Russian military vehicle in a desert convoy ramming a US armoured car, as a Russian helicopter flies low overhead.
Russia says the US obstructed a patrol.
A US defence official told BBC partner CBS News that Russian forces had entered a “security zone” that they had agreed to stay out of.
The White House said the vehicle’s crew sustained minor injuries in the collision.
News of the incident broke on Wednesday. There have been frequent interactions between US and Russian forces in Syria, but confrontations are considered rare.
The Russians back Syrian government forces while the Americans support local Kurdish fighters, in a civil war that has convulsed the country since 2011.