The Soyuz launch from the Baikonur cosmodrome in
The International Space Station
The Soviet-era Soyuz system will provide the world's only link for human travel to the ISS after the
Any problems with Soyuz spacecraft or rockets could pose a serious challenge to international space exploration.
The Russian Federal Space Agency said in a statement that a fault with one of the Soyuz capsule's systems had been uncovered in testing and that the launch would be delayed "until a later date".
Various news reports said the launch may now take place between April 7 and 10.
The delay was announced just two weeks after a top government official accused the space agency of committing "childish" errors that included the loss of three satellites in December.
RIA Novosti said the latest malfunction affected a switching system that allowed the crew to communicate with ground control.
"We have formed a task force involving the developers and producers as well as the parent organisation of the manned flight programme, RSC Energia," the space agency statement said.
The mission will include the Russians Alexander Samokutyayev and Andrei Borisenko as well as NASA astronaut Ronald Garan.