India's return to spaceflight as part of the Axiom-4 private mission has run into further delay as NASA announced on Thursday that it was examining a leak onboard the International Space Station's Russian module.

"NASA and Axiom Space are postponing the launch of Axiom Mission 4 to the International Space Station," a NASA statement said.

India's Shubhanshu Shukla and three others are part of the Axiom-4 commercial mission to the International Space Station.

The astronauts were originally scheduled for lift-off on May 29, which was put off to June 8, June 10 and June 11, when SpaceX, the providers of the launch rocket and the space capsule, detected a liquid oxygen leak in the Falcon-9 rocket.

On Thursday, NASA announced that it was working with Roscosmos to understand a new pressure signature, after the recent post-repair effort in the aft-most segment of the International Space Station's Zvezda service module.

"We appreciate all the incredible work of our customers, NASA, and SpaceX on this Mission. This is the right thing to do for Axiom Space, for NASA, and for our customers," Kam Ghaffarian, Executive Chairman and co-founder of Axiom Space, said in a statement.

"We will continue to work with all of our partners to finalise a new launch date and look forward to flying the Ax-4 Mission soon," he said.

"A new launch date for the fourth private astronaut mission will be provided once available," a joint statement from Axiom Space and NASA said, announcing the postponement of the launch of the Axiom-4 mission.

The statement said as part of an ongoing investigation, NASA was also working with Roscosmos to understand a new pressure signature, after the recent post-repair effort in the aftmost segment of the International Space Station's Zvezda service module.

"Cosmonauts aboard the space station recently performed inspections of the pressurised module's interior surfaces, sealed some additional areas of interest, and measured the current leak rate," the statement said The postponement of Axiom Mission 4 provides additional time for NASA and Roscosmos to evaluate the situation and determine whether any additional troubleshooting is necessary. NASA defers to Roscosmos to answer specific questions about the Zvezda module, the statement said.

The Russian Space Agency has been dealing with a cabin pressure leak at the station, and recent repairs resulted in what NASA calls a new pressure signature.

The three Russians aboard the space station recently inspected the inside walls of the ageing Zvezda service module, which was launched in 2000. They sealed some areas and measured the current leak rate.

Following this effort, the segment is now holding pressure, NASA said in an online update.

Former NASA astronaut and director of human spaceflight at Axiom Space Peggy Whitson will command the commercial mission, while Indian Space Research Organisation astronaut Shubhanshu Shukla will serve as pilot.

The two mission specialists are ESA (European Space Agency) project astronaut Slawosz Uznanski-Wisniewski of Poland and Tibor Kapu of Hungary.

The crew will lift off aboard the SpaceX Dragon spacecraft on Falcon 9 from Launch Complex 39A at NASA's Kennedy Space Center in Florida.

The 14-day mission will "realise the return" to human spaceflight for India, Poland and Hungary.

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