An unnamed armed group has shut a valve on a pipeline linking Libya's major Al-Sharara oil field to the coastal city of Zawiya, triggering a significant drop in crude production, the National Oil Corporation (NOC) said on Monday.

The disruption raises the risk of further losses to state revenues and could affect operations at the Zawiya refinery if the shutdown continues.

The NOC said pressure built up in the pipeline following the closure, forcing production at the Al-Sharara field to be reduced. 

The state oil company warned it could declare force majeure if the disruption persists, potentially suspending some contractual obligations because of circumstances beyond its control.

Located about 900 kilometers south of Tripoli, Al-Sharara is one of Libya's key oil-producing fields. 

Its pipeline connects the landlocked field with Zawiya, around 45 kilometers west of the capital, where a major refinery and oil-export infrastructure are located.

The NOC did not identify the armed group behind the shutdown. Libya has repeatedly faced disruptions to its oil industry as armed groups and protesters have targeted fields, pipelines and export facilities over political and economic demands.