A US KC-135 aerial refueling aircraft crashed in western Iraq, killing all six crew members, the US military said Friday, adding that the incident was not caused by "hostile fire."

The incident -- which took place Thursday and involved a second plane that landed safely -- brings the number of US troops killed in operations against Iran to at least 13.

"All six crew members aboard a US KC-135 refueling aircraft that went down in western Iraq are now confirmed deceased," US Central Command (CENTCOM), which is responsible for American forces in the Middle East, said in a post on X.