Russia will replace the Soyuz spacecraft set to take the next crew to the International Space Station after a fault was found in testing, a space industry source said Wednesday.

The Russian space agency had previously said that only a capsule used for the crew's re-entry to Earth would be replaced after tests found it was not hermetically sealed, delaying a mission originally set for March 30.

"A decision has been taken to completely replace the Soyuz TMA-04M ship, not just the damaged re-entry capsule," the source told the Interfax news agency, saying the crew would fly in a Soyuz built for the following mission, which will in turn be delayed.

The source said the decision was taken because it was easier to use an entirely new Soyuz than to switch the re-entry capsule, due to modifications to the hatch of the newer craft.

The Soyuz will be ready in the next two weeks and then tests at Russia's Baikonur cosmodrome in Kazakhstan will take a further six weeks, the source said.

The head of Roscosmos, Vladimir Popovkin, said Tuesday that the launch of the next Soyuz would be most likely be postponed until the end of April, with the final decision to be taken after talks with NASA on Thursday.

The fault in the Soyuz craft, which is now the only means to ferry crews to the ISS after the retirement of the US shuttle, is the latest in a series of embarrassing setbacks to Russia's space programme.