The oxygen supply system has failed in a module on the Russian segment of the International Space Station (ISS) but the crew is in no danger, Russian space agency Roscosmos said Thursday.

The oxygen supply system on the Zvezda module on the orbital lab failed late on Wednesday but a second system on the American segment is operating normally, a Roscosmos spokesperson told AFP.

"Nothing threatens the security of the crew and the ISS," said the spokesperson, adding this repair work to fix the issue would be carried out on Thursday.

The issue arose after three new crew -- two Russian cosmonauts and an American astronaut -- reached the ISS on Wednesday to bring the number of current crew on board to six.

The problem is the latest incident on the ISS -- whose first module was launched over two decades ago in 1998 -- after the crew in August detected an air leak on board.

Roscosmos emphasised at the time that the leak was not significant and posed no danger. But part of the problem was detecting precisely where it came from.

The crew believe that they have now found the source of of the leak. The Roscosmos spokesperson said that they would receive precise instructions from mission control to carry out future work on the problem.

Quoted by the RIA Novosti news agency, veteran Russian cosmonaut Gennady Padalka said that the Russian equipment aboard the ISS was well past its use-by date.

"All modules of the Russian segment are exhausted," said Padalka, who holds the world record for most days spent in space. He added that the equipment should only be used for 15 years whereas it was now two decades old.