Russian space officials are to begin preparations to raise Mir's orbit. It is a move that will be seen as a strong indication that Russia does not plan to abandon Mir later this summer.

Russia is under great pressure to quit the 13-year-old space station and divert its resources and attention towards the International Space Station (ISS), of which it is a member.

Nasa has expressed concern that Russia cannot operate Mir and meet its commitments to the ISS. Russia has signed an agreement saying that it will de-orbit Mir by the end of this summer.

But Russia shows every sign that it wishes to maintain the old station. Cosmonauts are in training that could occupy the space station for the foreseeable future.

Financial problems

The Russian Space Agency (RSA) has also been looking for investors who could afford the $250m a year it would take to keep Mir alive. On several occasions, the head of the RSA Yuri Koptev has said that investors have been found.

The first part of the ISS

Western analysts, however, dismiss these claims as kite-flying by Koptev to drum-up international interest in financing Mir.

The RSA had set the end of April as the deadline to find the money to pay for Mir. So far, no investor has been forthcoming.

But if Mir is boosted into a higher orbit, it will surely signal that Russia intends to keep it in orbit beyond the end of the summer - private backer or not.

Salamander deaths

Meanwhile, according to the French space agency CNES, six salamanders have died mysteriously on Mir. Parts of their tails will be brought back to Earth for analysis.

"Several theories have been put forward to explain their abrupt deaths, which were not preceded by any symptoms. Carbon dioxide poisoning cannot be ruled out,'' the agency said in a statement.

Four males died last week and two females on Monday, said Michel Viso, the scientist co-ordinating the experiments on salamander tail regrowth, inner ear development and sperm generation in males. Two females are left on Mir.

CNES said the salamanders' box was ventilated twice a day by French astronaut Jean-Pierre Haignere, who joined the station in February and who discovered the dead animals.