WASHINGTON, March 13 (Reuters) - All six crew members

aboard a U.S. military refueling aircraft that crashed in

western Iraq are confirmed to have been killed, the U.S.

military said on Friday.

A U.S. military refueling aircraft crashed in western Iraq

on Thursday, in an incident the military said involved another

aircraft but was not the result of hostile or friendly fire.

The deaths add to the seven U.S. service members who have

already been killed as part of U.S. operations against Iran

which began on February 28.

"The circumstances of the incident are under investigation.

However, the loss of the aircraft was not due to hostile fire or

friendly fire," a statement from U.S. Central Command said.

A U.S. official told Reuters that the second aircraft

involved in the crash, which landed safely, was also a military

refueling aircraft known as the KC-135.

The United States has deployed a large number of aircraft

into the Middle East to take part in operations against Iran and

the incident highlights the risk of not just operations, but of

refueling aircraft in the air.

The KC-135, built by Boeing ( BA ) in the 1950s and early

1960s, has served as the backbone of the U.S. military's air

refueling fleet and is critical to allowing aircraft to carry

out missions ​without having to land.

The Islamic Resistance in Iraq, an umbrella group of

Iran-backed armed factions, claimed ​responsibility for downing

the U.S. military refueling aircraft.

Reuters reported on ​Tuesday that ⁠as many as 150 U.S.

troops have been wounded in the U.S.-Israeli war on Iran. News

of the crash comes the same day two U.S. sailors were injured

after ⁠the ​USS Gerald Ford suffered a non-combat-related fire

on ​board.

The first seven U.S. troops were killed when a drone slammed

into a U.S. military facility in Port ​Shuaiba, Kuwait.

President Donald Trump and other senior officials have

warned the Iran conflict will result in more U.S. military

deaths as Tehran retaliates against U.S. and Israeli strikes.