A US Air Force Boeing KC-135 Stratotanker aerial refuelling tanker aircraft is seen in Ben Gurion international airport near Tel Aviv, Israel, in February.

An American military refuelling aircraft involved in the US operation in Iran has crashed in western Iraq, according to the US Central Command.

The US Central Command said "the incident occurred in friendly airspace during Operation Epic Fury", but that it was not the result of hostile or friendly fire.

Two aircraft were involved in the incident, a statement on Thursday said, as "one aircraft went down in western Iraq, and the second landed safely". Rescue efforts were under way, the statement added.

The plane was a military KC-135 refuelling plane, which typically play a major role in conflicts.

The KC-135 aircraft usually has a crew of a pilot, a co-pilot and a boom operator.

The status of the crew is unknown at this time, BBC's US partner CBS News has reported.

Since the outbreak of the US-Israel war with Iran, seven US soldiers have been killed in the conflict.

Speaking shortly after news of the incident emerged, Democratic Congressman Jim Himes told BBC Newsnight: "It's very early returns right now.

"A KC135 is usually used for refuelling. It carries a crew between 3-5 people. We pray that those 3-5 people are safe."

Himes is part of the "Gang of Eight" typically briefed by the White House on military operations.

He continued: "This is part of the inevitable cost of a conflict. Even the best military doesn't operate without accidents and that's what appeared to have occurred here."

The US military has now lost at least four aircraft during the war in the Middle East.

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 eject safely.

Refuelling tankers are responsible for keeping jets and bombers properly fuelled for combat that involve long distances to reach their targets.

The KC-135 Stratotanker was built by Boeing in the 1950s and early 1960s.

It has been a backbone to the US military's air refuelling fleet, and critical in allowing aircraft to carry out missions without having to land. (BBC, excluding headline)

•PHOTO: A US Air Force Boeing KC-135 Stratotanker aerial refuelling tanker aircraft is seen at an airport. PHOTO: EPA via BBC.

Update news