(Releads with second closure)
TUNIS, Aug 22 (Reuters) - Libya's Sharara oilfield, the country's largest, shut on Tuesday hours after reopening following a three-day pipeline blockade, an oil official said.
The shutdown was due to action by a different group to the one that caused a closure at a valve leading from Sharara to Zawiya terminal on Saturday, the official said.
A statement from National Oil Corp (NOC) announcing the end of the earlier shutdown and the lifting of force majeure on loadings of crude from Sharara at Zawiya was no longer available on its website.
Sharara, which has been pumping up to 280,000 barrels per day (bpd) in recent weeks, has been affected by repeated shutdowns because of protests by armed groups and oil workers.
The NOC said the closure that lasted from Saturday until Tuesday morning had occurred at valve 17 on the pipeline leading from Sharara to Zawiya. It did not say where the valve is located.
"No group has claimed responsibility for the valve closure, and no demands were made, but NOC engineers despatched to open the valve found a gearbox had been stolen," the statement said.
"This gearbox was removed by criminals for one purpose only, and that is to blockade the line in future," NOC Chairman Mustafa Sanalla was quoted as saying.
The NOC runs Sharara in a joint venture with oil companies Repsol, Total, OMV and Statoil .
The field's production is key to a revival in Libya's oil output, which surged above 1 million bpd in late June, about four times higher than its level last summer. (Reporting by Ahmed Elumami; Writing by Aidan Lewis; Editing by Dale Hudson and David Evans)