The centre's spokesman said the leak had been located in the Kvant-2 module containing research equipment. He said the loss of air pressure was within the admissible limits and did not pose any threat to the crew.

Cosmonauts have been forced to patch-up Mir on a number of occasions

The leak is the latest headache to afflict the 13-year-old space station.

Mir is due to be mothballed in August, shifting responsibility for a permanent presence in space to the International Space Station.

The station has suffered a series of accidents in recent years, including a crash with a cargo module in 1997, which pierced the hull and triggered a major emergency.

Russia's space agency is keen to keep Mir operational for as long as possible. But private sources of income that would keep the station flying have yet to be found.

Launch row

Plans for the station's fiery death are being complicated by a row between Russia and neighbouring Kazakhstan over rocket launches.

Baikonur launches have been put on hold by Kazakhstan

The Kazakh authorities want compensation for damage caused by the crash of a Russian Proton rocket on their territory last Monday.

Until the money is forthcoming and the cause of the rocket failure has been established, the Kazakhs have banned further launches from the Baikonur cosmodrome, delaying the despatch of vital spare parts to Mir.

On Saturday, Russian and Kazakh officials toured the crash scene by helicopter to assess the environmental damage caused by the rocket.

Russian space officials say that without the parts the crew may have to return to Earth and abandon the space station. That would mean no other crew would be able to return.

The Baikonur launch complex was built by the Soviet Union, but is now located in an independent Kazakhstan and has become the subject of years of argument between the two countries.