The U.S. Central Command said in a statement on Monday that a helicopter mishap in northeastern Syria has resulted in injuries to 22 service members.

The incident occurred on Sunday and caused injuries “of various degrees” to U.S. personnel.

No enemy fire was reported during the incident, and an investigation has been launched into the cause.

“The service members are receiving treatment for their injuries and 10 have been evacuated to higher care facilities outside of the CENTCOM AOR [area of responsibility],” the statement read.

U.S. Central Command-led coalition forces and partners forces are conducting operations against ISIS in the region “to prevent them from re-establishing any type of network or effective military effort,” CENTCOM said on June 6.