CAPE CANAVERAL - NASA delayed its first space shuttle launch of the year for a fourth time on Friday after failing to resolve concerns about a potential problem with fuel pressurisation valves.

Shuttle Discovery had been scheduled to lift off on Feb.27 for a 14-day flight to outfit the International Space Station with a final set of solar wing panels. The flight, already delayed three times for safety reviews, was not immediately rescheduled.

The issue that has delayed the mission involves three small valves in the shuttle's rear engine compartment that are needed to keep the external fuel tank properly pressurised during the 8.5-minute climb into orbit.

During the last shuttle mission in November a tiny piece of one valve cracked. There was no danger to the shuttle or its crew, but the US space agency wants to be sure a reoccurrence would not have a different outcome. -- REUTERS