Unidentified gunmen in Libya have waged an attack on the Al-Mabrook oil field in the central part of the North African country, the state-run National Oil Corp (NOC) says.

“Unknown gunmen stormed the Mabrook oil field last night,” NOC spokesman Mohamed El-Harari said on Wednesday without elaborating.

The development came as armed militant factions affiliated with the two rival governments in Libya fight for control of Libya nearly four years following the downfall of long-time ruler Muammar Gaddafi.

Work at the oil field, located south of the city of Sirte, came to a halt in December after armed clashes shut down the Es Sider oil port.

Sirte is the stronghold of the militant group Ansar al-Sharia. The area has been plagued by clashes as armed groups compete for control of the Es Sider and Ras Lanuf oil ports.

Meanwhile, French oil giant Total, which jointly operates the Al-Mabrook oil field with NOC, announced that it had earlier pulled out its staff from the facility.

The oil output of Libya, a member of the Organization of the Petroleum Exporting Countries (OPEC), has plunged to around 350,000 barrels per day (bpd), from 1.6 million bpd pumped during Gaddafi’s rule, according to the latest data.

Libya’s Tripoli-based General National Congress, backed by the Fajr (dawn) Libya militias and in control of the capital, is waging a war against the official Libyan army, supported by the Tobruk-based parliament, in the far east of the country.

The new Tripoli rulers have set up a rival parliament and government not recognized by the international community.