The California-based company SpaceX on Saturday scrubbed the launch of its Dragon capsule toward the International Space Station at the last second due to a rocket engine problem.

The abort came a half-second before lift-off due to high pressure in the centre engine of the Falcon 9 rocket, forcing a shutdown of the launch attempt. The next try is expected May 22 at 3:44 a.m. (0744 GMT).

The launch of the SpaceX Falcon 9 rocket, carrying the unmanned Dragon and over half a tonne of cargo toward the orbiting lab, would mark the first attempt to send a privately built spacecraft to the research outpost, where it plans to do a fly-under followed by a berthing.

SpaceX is the first of several U.S. competitors to try sending its own cargo-bearing spacecraft to the ISS with the goal of restoring U.S. access to space for human travellers by 2015.