Wednesday's statement by the National Oil Corporation says an unidentified group on Tuesday closed the pipeline linking the Sharara oilfield to the port of Zawiya, on the Mediterranean coast.
It says this is the second such closure breach of the pipeline in the last 10 days.
The field produces around 290,000 barrels a day worth $19 million. It's controlled by the self-styled Libyan National Army led by Khalifa Hifter.
However, the forces aren't in full control of the entire route of the pipeline, which runs partially through territories held by militias allied with the U.N.-supported government in the capital, Tripoli.