Twenty-two US soldiers were injured in a helicopter accident in northeastern Syria at the weekend that did not involve any reported enemy fire, US Central Command said on Tuesday.
"A helicopter mishap in northeastern Syria resulted in injuries of various degrees to 22 US service members" on Sunday, Centcom said in a statement.
"The service members are receiving treatment for their injuries and 10 have been evacuated to higher care facilities," it said.
"The cause of the incident is under investigation, although no enemy fire was reported."
The United States has about 1,000 troops deployed in Syria as part of international efforts to combat insurgents, and periodically carries out strikes targeting militants in the country.
US bases have been repeatedly targeted in the past year, with cells linked to the Islamic State (IS) group claiming responsibility for some of them.
In March the United States carried out air strikes on Iran-linked groups in Syria after a US contractor was killed in a drone attack on a US-led coalition base near the city of Hasakah in northeastern Syria.
At the time, the Syrian Observatory for Human Rights war monitor said at least 19 people were killed in the US air strikes.
Meanwhile, Commander of US Central Command Gen. Michael E. Kurilla met with Jordan's King Abdullah II on Monday, where issues such as defence enhancement, cooperation between Jordan and the United States, as well regional and international efforts to counter terrorism were discussed according to a statement.
US forces first deployed into Syria during the Obama administration's campaign against Islamic State, partnering with a Kurdish-led group called the Syrian Democratic Forces (SDF).
The conflict in Syria, which began over a decade ago, has killed over 500,000 Syrians and displaced millions more, as a result of a brutal crackdown and Assad regime bombardment on civilian areas.
Since then, Syria has plunged into poverty, with much of its infrastructure and economy devastated.