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, reports BBC.
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.
News of the incident broke on Wednesday and the Russian defence ministry said it had given the US military prior warning that it would be patrolling in the area.
"Despite that, in violation of existing agreements, the US armed forces soldiers tried to block the Russian patrol," said a ministry statement quoted by Tass news agency.
"In response to that, the Russian military police took necessary measures to prevent an incident and to carry on fulfilling the mission they had been given."
The White House National Security Council (NSC) said a Russian vehicle struck a US mine-resistant all-terrain vehicle, "causing injuries to the vehicle's crew".
An unnamed US military source told the Politico website that four US soldiers suffered mild concussion.
The US has about 500 troops in the area - far fewer than previously - to help secure it against any further threat from Islamic State (IS) jihadists. The US military is assisting the Kurdish-led Syrian Democratic Forces (SDF) alliance.
NSC spokesperson John Ullyot, quoted by Politico, said the incident occurred at about 10:00 local time on Wednesday, when a routine security patrol encountered Russian troops near Dayrick in north-east Syria.
Condemning the Russian military for colliding with a US vehicle, he said the coalition patrol then left the area "to de-escalate the situation".
"Unsafe and unprofessional actions like this represent a breach of de-confliction protocols, committed to by the United States and Russia in December 2019," Mr Ullyot said.
Russia has provided huge firepower, including heavy bombers, for Syrian President Bashar al-Assad's forces battling various rebel groups, including IS.