Bishkek, May 4 (IANS/RIA Novosti): A US military Boeing KC-135 refuelling aircraft crashed in a mountainous area in Kyrgyzstan for unspecified reasons, the US Air Force said. The fate of the crew remained unclear.

"A US Air Force KC-135 tanker aircraft crashed today (Friday) in northern Kyrgyzstan," the US Air Force's 376th Air Expeditionary Wing based in the country said.

The Boeing KC-135, also known as the Stratotanker, crashed into a mountain gorge about 60 km west of the capital Bishkek, a Kyrgyzstan interior ministry spokesman said.

Kyrgyz news website kloop.kg showed photographs of fragments of the aircraft displaying its tail number, AMC 38877.

"Emergency response crews are on scene. The status of the crew is unknown," the US Air Force said.

The head of the local emergencies ministry, Kubatbek Boronov, said there were three crew on board the plane, who have not been found.

Local law enforcement officials told kloop.kg they had likely been killed in the crash.

Locals reported seeing no parachutes in the vicinity of the incident. The Stratotanker usually has a crew of three, pilot, co-pilot and boom operator.

Local residents cited by Kyrgyz and Russian media gave conflicting versions of the incident, with some saying the aircraft fell apart in the air and others claiming it blew up on impact.

The cause of the crash was also unclear, though the burning debris covered a wide area, with the main part of the fuselage falling far from the tail, kloop.kg reported.

It said the aircraft's nose section, which houses two of the crew, had not yet been reached as it is some distance away in the mountains.

"The ground around the aircraft fragments is totally burned and there is a strong smell of fuel in the air," it said.

An employee at Manas airport said the crew of the aircraft had reported bad weather and thunder in the area at the time and had asked for permission to fly around towering cumulus clouds en route.

The Stratotanker was attached to the US Air Force base in Manas, Bishkek's international airport.

The base provided transit for American forces in Afghanistan since 2001, but is due to be shut down in 2014 because the Kyrgyz government refused to extend the lease.

One of the oldest designs flying in the USAF, the KC-135, derived from the Boeing 707 civil airliner, first entered srervice in 1957. It is due to be replaced by Boeing's KC-46.

According to the online airrefuelingarchive, and a historical study of KC-135 accidents by Chris Hoctor, a retired USAF Master Sergeant, the last crash of a KC-135 was in 1999.