"Am pushing launch back approximately a week to do more testing on Dragon docking code. New date pending coordination with NASA," Musk said in a Twitter post.

The company, also known as SpaceX, is expected to be the first private company to fly to the $100 billion research complex, which is owned by the United States, Russia, Europe, Japan and Canada.

With the retirement of the space shuttles last year, NASA is looking to SpaceX and Orbital Sciences Corp to take over flying U.S. cargo to the space station, which orbits about 240 miles above Earth. The companies hold combined contracts worth $3.5 billion for cargo delivery services.

Launch of SpaceX's Falcon 9 rocket and Dragon cargo capsule on SpaceX's trial run to the station was slated for April 30, but the mission is being delayed about a week to allow more time for engineers to test software needed for the capsule's berthing at the station, Musk said in his post.

Last week, NASA cleared SpaceX for launch on April 30, pending a final review of its flight software.

The company successfully launched and recovered a test Dragon capsule in December 2010.

SpaceX is among several firms vying to develop space taxis to fly astronauts to the station as well.

More information about a new launch date for SpaceX is expected later this week.

(Reporting by Irene Klotz; Editing by Sandra Maler)

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