Rescue operations are under way after a US military refuelling aircraft crashed in western Iraq, US Central Command (Centcom) has said.

Neither hostile nor friendly fire were involved in the downing of the KC-135, which occurred over western Iraq, Centcom said.

The tanker had been involved in ongoing US operations against Iran, and was one of two aircraft involved in the incident, the military command unit said. The second landed safely, it added.

The Boeing-manufactured aircraft are capable of refuelling planes midair and typically 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.

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

The status of the crashed plane's crew is currently unclear, according to the BBC's US partner CBS News.

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

Democratic Congressman Jim Himes, part of the so-called "Gang of Eight" US lawmakers typically briefed on military operations, appeared on BBC Newsnight shortly after news of the incident emerged.

He told the programme that it was too early to tell specifically what had led to the crash, but said: "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 added: "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 current 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 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.

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