June 13 (UPI) — Twenty-two U.S. service members were injured in a helicopter “mishap” in northeastern Syria, the U.S. military said late Monday.

The unspecified incident occurred Sunday, resulting in the service members sustaining injuries of varying severity, U.S. Central Command, which oversees American troops in the Middle East, said in a statement.

“The service members are receiving treatment for their injuries and 10 have been evacuated to higher care facilities” outside of Central Command’s area of responsibility, or AOR, it said.

“The cause of the incident is under investigation,” it said, while remarking no enemy fire was reported at the time of the so-called mishap.

The United States first deployed troops to Syria in 2015 to counter the Islamic State. There are roughly 900 U.S. troops operating in the Middle Eastern country in support of Operation Inherent Resolve, a joint task aimed at defeating the IS, according to a late 2022 Congressional Research Service report.

Last month, Central Command conducted 17 partner operations in Syria, resulting in 20 IS operatives detained and two killed, the U.S. military said in a summary of its May activities.

Despite IS’ territorial defeat four years ago, the terrorist organization and Iran-backed militias still pose a threat to U.S. service members in the Middle East.

In April, a U.S. base in northeastern Syria came under attack. Less than a month earlier, a drone struck a coalition base near Hasakah, injuring five U.S. service members that the Pentagon responded to with retaliatory airstrikes on sites used by groups affiliated with Iran’s elite Islamic Revolutionary Guard Corps.