The U.S. military said Thursday that a KC-135 military refueling plane was lost while flying over Iraq in an incident that was “not due to hostile or enemy fire.”

The U.S. Central Command said in a statement that the incident involved two aircraft and occurred in friendly airspace. One of the aircraft went down in western Iraq, and the second landed safely, it added.

“The incident occurred in friendly airspace during Operation Epic Fury, and rescue efforts are ongoing, the the U.S. Central Command said, referring to the war against Iran, which led to retaliatory strikes by Tehran across the Middle East.

It was unclear how many U.S. service members were on board the KC-135 refueling aircraft that crashed.

The Islamic Resistance in Iraq, a group of militias in the country backed by Iran, claimed responsibility for the downing of the U.S. aircraft in a statement posted on its Telegram channel.

This is the fourth reported aircraft loss since the Iran war started, after three F-15 fighters were shot down by friendly fire from Kuwait’s air defenses.

The KC-135, which cost $39.6 million in 1998 according to the U.S. Air Force, is normally used to refuel other aircraft in mid-air.

Source: CNBC