BENGHAZI, Libya - Libya's Sharara oil field, the country's largest, has been closed since late on Sunday, an engineer at the field and a Libyan oil source said.

They did not disclose the reason for the shutdown but a trading source said it was linked to a protest over salary demands.

Sharara, which had been producing up to 280,000 barrels per day (bpd), has been affected by repeated shutdowns or partial shutdowns this year caused by blockades imposed by armed groups, security problems and protests.

Sharara is crucial to a recovery in Libya's oil output that saw production rise to above 1 million bpd in June, more than four times its level in mid-2016.

Libya is exempt from OPEC-led oil production cuts, and the North African country's revival has complicated the bloc's efforts to bolster global prices.

Libya was producing more than 1.6 million bpd before a 2011 uprising led to a political and armed conflict that badly disrupted its oil industry.

Production continues to be hampered by budget constraints and infrastructure damage, as well as groups that trigger shutdowns to press local demands.

Last month a group from southwest Libya, near Sharara, threatened to close the field over the detention in Tripoli of two members of a political delegation, though the two-day ultimatum they set passed without the field shutting.

Libya's National Oil Corporation (NOC) operates Sharara in partnership with oil companies Repsol , Total , OMV and Statoil .

(Reporting by Ahmad Ghaddar and Ayman al-Warfalli; writing by Aidan Lewis; editing by Jason Neely) ((Aidan.Lewis@thomsonreuters.com ; +216-29850352;))