A U.S. KC-135 tanker aircraft crashed in western Iraq on Thursday, killing all six people on board.
In a statement, U.S. Central Command (CENTCOM) said the Stratotanker went down around 2 p.m. ET in an incident involving another airplane. The other aircraft landed safely.
The crash was not caused by “hostile fire or friendly fire,” officials said.
Early Friday morning, CENTCOM confirmed that four of the six crew on board the KC-135 were killed and said rescue efforts were still under way. Around 10 a.m., the command confirmed that all six crewmembers had died.
The cause of the crash is now under investigation. CENTCOM said it will not release the names of those killed until 24 hours after their families have been notified.
U.S. forces in the Middle East have been engaged in operations against Iran since February 28. It was not immediately clear if the KC-135 was flying in support of those operations when it went down.
Thursday’s crash marks the fourth crewed U.S. aircraft lost since the conflict began. On March 1, three F-15E strike fighters were mistakenly shot down by Kuwait, a U.S. ally. All six crew ejected safely.