WASHINGTON (Reuters) - NASA and Boeing delayed the launch of Boeing's Starliner crew capsule again on Friday, giving them four more days to assess a helium leak before attempting to launch the spacecraft's first two astronauts into space, the space agency said Friday.

Starliner's liftoff from Florida has been delayed several times in May and it was last scheduled for May 21.

Aside from the helium leak, a technical issue with its Atlas 5 rocket had prompted an earlier delay. The program is several years behind schedule and more than $1.5 billion over budget.

The latest postponement will give more time "to finalize next steps that address a stable helium leak", NASA said. The launch is now targeted for no earlier than 3:09 p.m. EDT (1909 GMT) on Saturday, May 25.

Boeing has been developing Starliner for more than a decade to provide NASA with a second U.S. spacecraft capable of ferrying astronauts to and from the International Space Station. SpaceX's Crew Dragon capsule, built under the same NASA program, first launched astronauts to space in 2020.

Starliner's latest mission, called the Crewed Flight Test, is due to be the final test before the spacecraft is certified by the U.S. space agency to fly routine astronaut missions to the ISS. Boeing completed an uncrewed Starliner trip to the ISS in 2022 following years of technical and management issues.

(Reporting by Joey Roulette, Editing by Franklin Paul and Raju Gopalakrishnan)