A spacewalk by two Russian cosmonauts aboard the International Space Station (ISS) has been shelved after a coolant leak was detected, NASA said on Thursday.

The mission was called off just as it was about to get underway on Wednesday after technicians noticed liquid coming from a docked Soyuz spacecraft, a NASA webcast showed.

The Russian space agency, Roscosmos, said that the routine involving Sergei Prokopyev and Dmitry Petelin had been halted after one of the warning indicators alerted flight controllers to the problem.

NASA, meanwhile, said that a leak was seen coming "from the aft [rear] end of the Soyuz MS-22 spacecraft."

"NASA and Roscosmos will continue to work together to determine the next course of action following the ongoing analysis," NASA said. "The crew members aboard the space station are safe, and were not in any danger during the leak."

Rare US-Russia cooperation amid war in Ukraine

US astronaut Frank Rubio flew to the space station with the two Russian cosmonauts on the Soyuz rocket, which launched on September 21 from Kazakhstan.

Space has remained a rare example of cooperation between the United States and Russia since Moscow troops invaded Ukraine in February. The uneasy cooperation has so far held although Russia said earlier this year that it planned to withdraw from the project in 2024 and launch its own space station.

The ISS was launched in 1998 at a time of hope for Moscow-Washington relations following the Space Race amid the Cold War. Though nominally a global project, it was conceived by and is most reliant on the US and Russia to function.

jsi/msh (AFP, dpa, Reuters)