All countries taking part in the ISS program "agree that the program is underfinanced," added Sergei Gorbunov, a spokesman for the Russian space and aviation agency, Rosaviacosmos.

However, there was hardly any chance the countries cooperating with Russia on the ISS would come up with such a sum, Gorbunov said. "None of them has offered any funding," he said.

Moscow admitted for the first time Thursday that it would have to fund extra flights to the ISS following the United States' decision to ground its shuttle program.

The Russian government decided to earmark an additional 1.2 billion rubles (38 million dollars, 35 million euros) in budgetary funds to the space program over the next six months.

And Rossiya state television said that Russia may spend an additional 2.8 billion rubles (89 million dollars, 83 million euros) on its space program next year.

"No matter what agreements we might be able to reach with our international partners, there is no doubt that the main burden rests with us," Prime Minister Mikhail Kasyanov said in televised remarks.

"We have to guarantee -- although we hope this is only temporary -- the launches and future flights to the stations. This requires additional funding," he added.

Two US astronauts and one Russian cosmonaut arrived on the ISS for a four-month mission in early December and are eagerly watching the financial negotiations in Moscow as their supplies gradually run down.

Forty astronauts were to have visited the ISS in 2003 onboard two Russian Soyuz rockets and five US shuttles while three Russian Progress cargo craft were to deliver supplies and nudge the station into a higher orbit.

But after the Columbia space shuttle disintegrated on February 1, NASA halted the flights. Russia's manned Soyuz and cargo Progress craft are now the only way for transporting crew and supplying the ISS.

SPACE.WIRE