Field manager Hassan al-Sideek said bandits forced a valve to close from Sharara, blocking 40 percent of the delivery of crude oil to the Zawia oil refinery and terminal, the Libya Herald reported Monday.
Operations at Sharara, in the western Libyan desert, were shuttered in October by regional protesters calling for more local authority. The field has the capacity to produce 350,000 barrels of oil per day.
In January, Libyan Oil Minister Abdelbari al-Arusi said the restart of the Sharara oil field in the west of the country had contributed to recent production gains.
Maintenance crews were told by gunmen near the pipeline the rebels would only speak with government officials.
"We don't know what they want," a source told the Herald.
Libyan oil production flirted with the pre-war level of 1.6 million bpd in 2012 but has struggled to stay at more than 1 million bpd in recent years.