CAIRO (AP) — Libya’s national oil company said Sunday that an armed group has shut down two crucial oil fields, causing the country's daily production of oil to drop by 330,000 barrels.

The state-run National Oil Corporation said the group closed pump valves at the Sharara field, Libya’s largest, and el-Feel, effectively stopping production in both areas. Before the shutdown, Libya’s production of oil was at around 1.2 billion barrels per day.

Company head Mustafa Sanallah announced a force majeure, a legal maneuver that lets a company get out of its contracts because of extraordinary circumstances.

He said the closures cost Libya more than $160 million ($34.6 million) per day in lost revenues.

Sanallah said the NOC has urged public prosecutors “to take deterrent measures” and reveal “the planners, executors and the beneficiaries” of the shutdown. The same militia disrupted oil production at both fields in 2014 and 2016, he added.

An oil official in the capital Tripoli said the militia that shut down the fields is from the mountainous town of Zintan, around 136 kilometers (over 84 miles) southwest of Tripoli.

Tribal leaders in the area were negotiating with the militia leaders to allow the resumption of oil production, said the official, who spoke on condition of anonymity because he was not authorized to brief the media.

The shutdown came as the Russian invasion of Ukraine has shaken markets worldwide, causing crude oil prices to soar above $115 per barrel.

Libya has the ninth largest known oil reserves in the world, and the biggest oil reserves in Africa.

The dizzying developments in Libya’s oil fields have come amid a mounting standoff between two rival governments which threaten to again drag the country into chaotic infighting.