The assertion by the director of Russia's Federal Cosmic Agency, Anatoly Perminov, signified the increased strain between Washington and Moscow over the United States' reliance on Russian Soyuz spaceships to get its astronauts to the ISS.

"This is our position: if in 2005 the Americans want to fly aboard Soyuzes, let them pay the cost of these flights," Perminov told the ITAR-TASS news agency.

The United States has had no means of its own to transport people into space since it froze its space shuttle programme following the Columbia accident in February 2003.

While Russia and the United States have agreed to split the cost of getting people and materials to the ISS, the burden has in reality fallen on Moscow, Russian officials say.

A principal reason is that the United States' Iran Nonproliferation Act prohibits US funding for the Russian space program because of Moscow's nuclear and other military cooperation with Tehran.

On Wednesday Perminov said it was time for Russia to concentrate on developing its own section of the ISS.

"Starting in 2005 the priority will become developing the Russian segment and ensuring the activity of the Russian crew," Perminov said.

His comments came as Russian and US scientists investigated a brief loss of radio contact with the ISS' current crew, American Michael Finke and Russian Gennady Padalk, and a deviation in the station's orbit when the two stepped outside the station on a maintenance mission on Wednesday.

During the mission equipment was installed that will enable a European cargo vessel to dock alongside next year.

SPACE.WIRE