Nasa delayed its first shuttle launch of the year for at least a week to allow time for engineers to review a potential problem with valves that keep the fuel tank pressurised, according to managers.

The shuttle Discovery and seven astronauts had been scheduled to launch on February 12 to deliver a final set of solar wing panels to the International Space Station.

The mission was postponed until at least February 19 due to an issue with the valves that keep hydrogen fuel properly pressurised for the shuttle's three main engines.

"For the main engines to run correctly, the hydrogen tank has to be properly pressurised," said shuttle programme manager John Shannon.

During Nasa's last shuttle flight in November, a tiny piece of one valve broke off. That posed no threat to the shuttle but Nasa wants more time to consider what would happen if a bigger piece of the valve's lip breaks off or if a similar event were to occur at a different time during liftoff.

"We want to make sure we got this right," Dr Shannon said. "This has important consequences for us."