A United States 'spy plane' has made an emergency landing in eastern Russia, it has emerged today.

The surveillance Boeing OC-135B aircraft was flying a mission over Siberia as allowed under the Treaty on Open Skies when it reported a problem with its landing gear.

The unarmed plane made an emergency landing at Khabarovsk airport, but a military source in Russia has questioned whether the technical glitch was genuine.

The surveillance Boeing OC-135B aircraft (pictured) was flying a mission over Siberia as allowed under the Treaty on Open Skies when it reported a problem with its landing gear

The unarmed plane made an emergency landing at Khabarovsk airport (pictured), but a military source in Russia has questioned whether the technical glitch was genuine

Under the treaty, signatories are allowed to overfly the skies of each other gathering information about military forces and activities of concern to them.

The American military aircraft had left after a stopover in Ulan-Ude, in the Republic of Buryatia, and was due to fly north to Yakutsk, capital of Siberia's diamond-rich Sakha Republic.

Instead, after take-off the crew noticed the problem and the Boeing went east and made a landing 1,660 miles away in Khabarovsk.

An airport official confirmed Wednesday's emergency landing in the city, close to the Chinese border.

'A foreign aircraft made a forced landing in Khabarovsk. All emergency ground services have arrived on site. The flight landed safely at 3pm local time,' said a statement.

Earlier, the Russian Defence Ministry's Nuclear Risk Reduction Centre had announce the US Boeing OC-135B aircraft's observation flight over Russian territory between July 25 and 30.

An army source suggested the malfunctioning was 'not coincidental', and perhaps related to recent military exercises in the area.

A United States 'spy plane' has made an emergency landing in eastern Russia, it has emerged today

'They were due to go direct from Ulan-Ude north-northeast to Yakutsk,' said the unnamed source, as reported by The Siberian Times.

'Just imagine the kind of loop they needed to make to request the landing at approximately the same distance, but to the east?'..

The Boeing OC-135B aircraft seats up to 35 people as it monitors foreign territory on behalf of the US government.

One vertical and two oblique KS-87E framing cameras are used for low-altitude photography approximately 900 metres above the ground, and one KA-91C panoramic camera, which scans from side to side to provide a wide sweep for each picture used for high-altitude photography at approximately 11,000 metres.

The Treaty on Open Skies was signed in March 1992 and was seen as a major confidence-building measure after the Cold War.

It entered into force on January 1, 2002.

Currently 34 states are party to the treaty, including Russia and most NATO members