"The next possible launch opportunity is still being discussed," the US space agency said in a statement Tuesday.

The postponement of the launch, which had been set for Saturday, marks the third delay this month for the highly anticipated mission, which would allow NASA to certify a second commercial vehicle to carry crews to the ISS, beyond Elon Musk's SpaceX.

Earlier this month, the Starliner launch was postponed just hours before liftoff, with the astronauts already strapped in, due to a separate technical issue.

Then last week, another delay was announced to allow teams to further assess a helium leak linked to the service module, which sits on top of the rocket.

"The team has been in meetings for two consecutive days, assessing flight rationale, system performance, and redundancy," NASA said Tuesday. "There is still forward work in these areas."

The postponements come as the Starliner program faces years of delays and at a challenging time in general for Boeing, which is separately facing safety questions around its commercial aviation arm.