US space agency NASA says it will look into underlying problems after it was forced to once again postpone the launch of a next-generation rocket carrying an unmanned spacecraft into the moon's orbit.

NASA called off its latest attempt to launch the rocket on Saturday. It was the second postponement in a week. The launch was initially planned for Monday at the Kennedy Space Center in the state of Florida.

The agency stopped Saturday's countdown because liquid hydrogen fuel had leaked from the rocket's engine.

The next-generation Space Launch System rocket has been developed for the Artemis program, an international lunar exploration project aimed at sending astronauts to the lunar surface by 2025. NASA's new Orion space capsule is attached to the rocket.

Artemis is the first attempt to send astronauts to the moon since the Apollo program of the late 1960s and early 1970s. Japan and some European countries are among the participants in the US-led effort.

Agency officials said the new launch is expected to take place in the second half of this month at the earliest.