U.S. officials say the three crew members aboard the International Space Station were briefly evacuated to a Soyuz spaceship when a piece of debris threatened to strike the station.

The U.S. space agency, NASA, said crew members on Thursday locked down the hatches in the Soyuz and prepared the ship to leave the station if necessary. After the debris passed without incident, the astronauts returned to the space station.

Officials said the move was a precaution and the probability of impact was low.

On Wednesday, NASA delayed the launch of the space shuttle Discovery, blaming the delay on a hydrogen gas leak.

NASA said the launch from the Kennedy Space Center in the U.S. state of Florida, first planned for late Wednesday, will now take place no earlier than Sunday, March 15. A statement said the exact launch date is dependent on the work necessary to repair the problem.

The shuttle mission is planned to boost the power supply of the International Space Station.

The 14-day mission is to include four spacewalks, in part to install another set of solar panels for the orbiting outpost. The crew is also to inspect the station's heat shields and perform maintenance work.

The Discovery mission is also to deliver a new space station crew member, Koichi Wakata, who is to be the first Japanese crew member at the space station. He is to replace American astronaut Sandra Magnus, who is scheduled to return to Earth on the shuttle.

Some information for this report was provided by AP and Reuters.