Russian cosmonaut Salizhan Sharipov and US astronaut Leroy Chiao were due to leave on October 11 aboard a Soyuz space craft to replace the current crew, American Michael Finke and Russian Gennady Padalk, who have been orbiting aboard the ISS since April 21.

But on Tuesday, Vyacheslav Mikhailichenko, a spokesman for the Russian space agency, said the launch had been delayed "because of a malfunction in one of the rocket's systems, detected during tests."

"The decision on the exact date of the launch will be made within the next few days," he said.

It was the second delay of the Soyuz launch, which was originally due to blast off on October 9 but was pushed back two days because of a technical malfunction in the docking system.

A third team member, Russian Yury Shargin, will also take off from the Baikonur space station in the former Soviet republic of Kazakhstan, to spend 10 days aboard the ISS.

Russia, the United States and the European Space Agency are among the main partners in the 16-nation ISS project.

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