U.S. Central Command (CENTCOM) confirmed Friday that four U.S. service members were killed in a KC-135 aircraft refueling crash Thursday at about 2 p.m. in an incident that was neither friendly nor hostile fire. The incident took place in western Iraq, where four bodies were recovered, while search and rescue efforts have been undertaken to recover two missing crew members.

This brings the number of U.S. servicemen killed since the start of Operation Epic Fury on Feb. 28 to 11, with six killed in Kuwait by Iranian forces and one in Saudi Arabia. It also brings the number of aircraft crashes publicly confirmed by the United States to four. Three F-15E Strike Eagles were shot down by friendly fire in Kuwait, but all six crew members safely ejected.

CENTCOM issued a statement on X confirming the incident.

“At approximately 2 p.m. ET on March 12, a U.S. KC-135 refueling aircraft went down in western Iraq,” CENTCOM posted. “Four of six crew members on board the aircraft have been confirmed deceased as rescue efforts continue. The circumstances of the incident are under investigation.”

“However, the loss of the aircraft was not due to hostile fire or friendly fire,” the statement confirmed. “The identities of the service members are being withheld until 24 hours after next of kin have been notified.”

U.S. officials believe the crash may have been due to a mild collision but are still investigating. Iran took responsibility for shooting down the aircraft, but U.S. officials say there is no evidence to support that claim.

Rescue and recovery missions, called Tactical Recovery of Aircraft and Personnel (TRAP) missions, are dangerous, as rescuers race to the site of the crash to secure the area before enemy forces can deploy there to rescue service members or recover remains and retrieve or destroy sensitive equipment before it can fall into enemy hands.