The crew was scheduled to launch on the last mission to the International Space Station but was scrubbed [Reuters]

US space agency NASA has postponed the launch of space shuttle Endeavour for at least three days citing technical problems.

The shuttle had been due to lift off from Cape Canaveral in Florida on Friday.

The delay disappointed throngs of spectators and the US president, Barack Obama and his family who visited the Kennedy Space Center.

Mike Leinbach, the NASA launch director, said the next try for the launch would be Monday at the earliest.

Technicians will have to crawl into the engine compartment to track a suspected electrical short in a power distribution box.

"We'll fly no orbiter before it's time, and today she just wasn't ready to go," Leinbach said.

Late on Friday morning, one of the two prime heaters for a fuel line feeding one of Endeavour's three auxiliary power units failed. At the same time, another heater was acting up.

Leinbach said both main heaters need to be operating for redundancy. The power units provide hydraulic pressure to the main engines at liftoff and to the rudder and speed brake during landing.

The short appears to be in a switchbox or an electrical line leading to it, Leinbach added.

Obama was also supposed to meet Gabrielle Giffords, the mission commander's wounded wife. Giffords, who is an Arizona congresswoman, is recovering from a gunshot wound to the head, and has been at Cape Canaveral since Wednesday to attend her husband's launch.

Giffords hasn't been seen publicly since the January 8 assassination attempt, and left her Houston rehabilitation hospital for the first time to travel to Florida. It is not immediately known whether she would stay for another try or return to Houston.

Endeavour's upcoming mission to the International Space Station is the last in its 19-year history. It will deliver a $2bn physics experiment.

The shuttle, the youngest in the fleet, was built to replace Challenger, destroyed during lift-off in 1986, and made its maiden voyage in 1992.

Source: Agencies