CHRIS DRZAZGOWSKI/U.S. AIR FORCE/HANDOUT VIA REUTERS

U.S. Air Force Airmen from the 28th Expeditionary Air Refueling Squadron conduct a pre-flight brief outside of a KC-135 Stratotanker, in August 2019. All six crew members aboard a U.S. military KC-135 refueling aircraft that crashed in western Iraq are confirmed to have been killed, the U.S. military said today.

WASHINGTON >> All six crew members aboard a U.S. military KC-135 refueling aircraft that crashed in western Iraq are confirmed to have been killed, the U.S. military said today.

The 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.

Speaking with reporters at the Pentagon today, U.S. Defense Secretary Pete Hegseth said operations against Iran would continue.

“War is hell. War is chaos, and as we saw yesterday with the tragic crash of our KC-135 tanker, bad things can happen,” Hegseth said.

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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. The incident highlights the risk of not just operations but also of refueling aircraft in the air.

The KC-135, built by Boeing 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. The crash happened 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 and in another attack in Saudi Arabia.

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.