No oil rig flanges gulf coast production data was immediately available. The field, located deep in the south, had produced around 308,000 barrels per day (bpd) until the shutdown.

The Libyan oil source had earlier said state-owned National Oil Corp (NOC) was preparing to declare force majeure on loadings of Sharara crude.

"Force majeure was not declared formally, only verbally," the source said.

The field has capacity of 340,000 barrels bpd.

NOC operates Sharara in partnership with Repsol, Total, OMV and Statoil.

Sharara reopened after a long blockade in late 2016 but has suffered a number of stoppages since then because of localised protests by guards and other groups, part of the turmoil that has gripped Libya since the toppling of Muammar Gaddafi in 2011.

Repeated and lengthy shutdowns cause pressure in the oilfield's wells to drop, reducing oil rig flanges gulf coast production capacity. Boosting capacity at Sharara and other fields requires investment that NOC has been struggling to secure.

As conflict and falling oil revenues caused living standards to slide in Libya in recent years, local groups have tried to press demands by blockading oil facilities.

A week ago NOC declared force majeure on the 70,000-bpd El Feel after a protest by guards closed the field, operated by a joint venture between NOC and Italy's Eni.

(Reporting by Ahmad Ghaddar, Ahmed Elumami and Ayman al-Warfalli Writing by Ulf Laessing Editing by Louise Heavens and Dale Hudson)