All six crew members aboard a US military KC-135 refuelling aircraft that crashed in western Iraq are ​confirmed to have been killed, the US military said on Friday.

The refuelling 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 US service members who have been ​killed as part of US attacks on 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 US Central Command said.

Speaking ​with reporters at the Pentagon on Friday, US Defence 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.

A US official told Reuters that the second aircraft involved in the ​crash, which landed safely, was also a military refuelling aircraft known as the KC-135.

The United States ​has deployed a large number of aircraft into the Middle East to take part in war on Iran. ‌The ⁠incident highlights the risk of not just operations but also of refuelling aircraft in the air.

The KC-135, built by Boeing in the 1950s and early 1960s, has served as the backbone of the US military’s air refuelling fleet and is critical to allowing aircraft to carry out missions without having ​to land.

The Islamic Resistance ​in Iraq claimed responsibility for downing the US military refueling aircraft.

Reuters has reported that as many as 150 US troops ​have been wounded in the US-Israeli war on Iran. The crash ​happened the same ⁠day two US sailors were injured after the USS Gerald Ford suffered a non-combat-related fire on board.

The first seven US troops were killed when a drone slammed into a US military facility in Port ⁠Shuaiba, ​Kuwait and in another attack in Saudi Arabia.

US President Donald Trump ​and other senior officials have warned the Iran conflict will result in more US military deaths as Tehran retaliates against ​US and Israeli strikes.