All six members of a US military refuelling aircraft’s crew have now been confirmed dead after it crashed in western Iraq, US Central Command (Centcom) has said.

The US initially said it had located four of the deceased crew. It said neither hostile nor friendly fire were involved in the loss of the KC-135 aircraft on Thursday.

The tanker had been involved in ongoing US operations against Iran and was one of two aircraft involved in the incident. The second landed safely.

The Boeing-manufactured aircraft are capable of refuelling planes midair and play a major role in US military operations. They were used extensively in the first Gulf War to extend the range of fighter jets and bombers.

Centcom said the incident occurred at about 14:00 ET (19:00 GMT) on Thursday and that the circumstances of the crash were now under investigation.

A search and rescue operation was then launched to locate the remaining two crew members.

The US military command unit added that the identities of the personnel who had been killed were being withheld for 24 hours so their next of kin could be notified.

Gen Dan Caine, chair of the US Joint Chiefs, told a news conference on Friday that the plane had crashed “while the crew was on a combat mission”.

US Defense Secretary Pete Hegseth hailed the aircraft’s crew members as “American heroes”, stressing that their “sacrifice will only recommit us to the resolve of this mission”.

The KC-135 usually has a crew of at least a pilot, a co-pilot and a boom operator responsible for controlling the refuelling arm of the aircraft.

Centcom earlier described the crash as happening over friendly airspace – but this is a region of Iraq where pro-Iranian militias operate. Iran’s military claimed on state TV that an allied group had targeted the plane with a missile.

Thursday’s crash brings the official US military death toll in the US-Israel war with Iran, which began a fortnight ago, to 13.

The US military has now lost at least four aircraft during the current war.

Earlier this month, three F-15s were shot down in “an apparent friendly fire incident” over Kuwait, officials said. All six crew members were able to safely eject.

Boeing manufactured the KC-135 Stratotanker for the US military in the 1950s and early 1960s.

It has been a backbone to the US military’s air refuelling fleet, and allow combat aircraft to carry out longer missions without needing to land.