Production has resumed at four key oil fields in Libya after a three-week shutdown by gunmen linked to Libya's Petroleum Facilities Guard (PFG), the group said Tuesday.

The PFG-affiliated fighters had closed Al-Sharara, Al-Fil, Al-Wafa, and Al-Hamada fields in December over a pay dispute, cutting output from Libya by over 300,000 barrels per day, according to the National Oil Corporation.

On Tuesday, a PFG official said the sites in southwestern Libya, along with pipelines delivering oil and gas to export terminals on the country's northwest Mediterranean coast, "are operational again."

"The government has listened to our legitimate demands, which were financial and technical in nature," the official told AFP on condition of anonymity.

"We have been working in difficult conditions for years," he added.

This comes one day after PFG representatives met in Libya's capital, Tripoli, with interim Prime Minister Abdul Hamid Dbeibah, who "ordered the immediate reopening of the fields", according to a statement from his office.

Dbeibah also ordered a committee to look into "the difficulties [the PFG] faces in fulfilling its mission," the statement read.

Since the 1970s, Libya has depended heavily on revenues from its vast crude reserves.