Twenty-two US service members were injured in a helicopter "mishap" in northeast Syria, the US Central Command said late on Monday.
Ten service members had been evacuated to higher care facilities outside the Central Command area of responsibility, it said in a statement.
The cause of the incident on Sunday was under investigation, although no enemy fire was reported, said the US Central Command, which oversees US forces in the Middle East.
In March, 23 US troops in Syria suffered traumatic brain injuries during two attacks by Iran-backed armed groups, it said in April.
