An electrical malfunction has forced the US space agency to delay until Thursday the shuttle Discovery's final mission to the International Space Station, NASA said.

"Space shuttle Discovery's launch on the STS-133 mission has been delayed until no earlier than Thursday," NASA said in a statement.

The mission, initially scheduled for Monday, has been postponed three times.

Earlier delays were announced so that Kennedy Space Center technicians could repair quick-disconnect fittings in the system used to pressurize one of Discovery's orbital maneuvering rocket engines.