The US company SpaceX on Wednesday said it was unlikely to meet a planned May 7 launch to send its Dragon space capsule to the International Space Station, but did not set a new date for the attempt.
"At this time, a May 7th launch appears unlikely," spokeswoman Kirstin Grantham said in a statement.
"SpaceX is continuing to work through the software assurance process with NASA. We will issue a statement as soon as a new launch target is set."
Asked for further details, Grantham said May 10 was a possibility, but if not the delay may last a week or more. A new launch date was expected to be in place by Friday, she added.
SpaceX aims to be the first private company to send its own spacecraft to the orbiting research lab on a cargo mission.
The Dragon spacecraft has also been built to carry humans to space, and the company, owned by Internet entrepreneur and PayPal co-founder Elon Musk, hopes that a successful cargo trip to the ISS will soon lead to a manned mission.
The end of the US space shuttle program last year left Russia as the sole nation capable of sending astronauts into orbit.