Russia plans to postpone its next manned launch to the International Space Station (ISS) by at least a month, the head of its space agency's manned programmes told the RIA Novosti news agency Tuesday.

The current mission on the ISS is likely to land around 45 days later than the scheduled March 16, while the next mission set for March 30 will blast off with a similar delay, the Roscosmos official, Alexei Krasnov, said.

"I think their return and the launch of the next crew will be pushed back by a month or a month-and-a-half," Krasnov said, adding that he would have the exact dates after a teleconference with NASA set for Thursday.

Krasnov said that delays came after the re-entry capsule of the Soyuz TMA-04M space ship to be used in the mission was shown in testing not to be hermetically sealed and could not be used for safety reasons.

That means the next mission will have to replace it with the re-entry capsule intended for the following mission scheduled May 30, which in turn will be delayed.

Krasnov said the delays would not be a problem because the crew currently on the ISS had initially been assigned an "unusually short expedition" of 120 days.

The re-entry capsule goes inside the spacecraft and is the portion that eventually returns the astronauts to Earth when the mission is over.

Russia now has sole reponsibility for taking US and other international astronauts to the ISS following the withdrawal of the US space shuttle but its own space programme has been hit by a string of problems in recent months.