Four U.S. service members have been injured following an incident with Russian forces in northeast Syria.

Dramatic footage shared online shows an altercation between U.S. and Russian military vehicles. While it is hard to say what prompted the incident, vehicles from the U.S. and Russia can be seen slamming each other as Russian helicopters hover overhead.

One particularly intriguing video shared on Twitter shows an American M-ATV and MaxxPro MRAP being overtaken by Russian Typhoon-K, Tigr, Tigr-M SpN, Ural-4320, and BTR-82A vehicles. The vehicles can be clearly seen hitting each other as they drive through an arid area.

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According to Politico, four U.S. troops were diagnosed with mild concussion-like symptoms after the altercation.

In a statement discussing the incident, National Security Council spokesperson John Ullyot appeared to blame the Russian forces.

“Unsafe and unprofessional actions like this represent a breach of de-confliction protocols, committed to by the United States and Russia in December 2019,” he said. “The Coalition and the United States do not seek escalation with any national military forces, but U.S. forces always retain the inherent right and obligation to defend themselves from hostile acts.”

Russian and U.S. forces have operated in close proximity to each other during Syria’s long-running civil war. U.S. officials assert that Russian forces have encroached on U.S. troop-controlled territory in eastern Syria during recent months in an attempt to squeeze the U.S. military out of the region.

This incident comes just a few months after video emerged appearing to show a U.S. military vehicle pushing a Russian armored truck off the road.