Washington  - The launch of the space shuttle Discovery planned for later Wednesday was abruptly cancelled just hours ahead of blast off.

The launch had already been delayed for weeks to allow NASA time to examine valves that control the flow of gaseous hydrogen from the spacecraft's engine to its external fuel tank. A valve was found to be damaged after the space shuttle Endeavour's November flight, prompting NASA to delay Discovery's mission as a precautionary measure. (dpa)