But after Arab states including Egypt and the United Arab Emirates cut ties with Qatar last week, east Libyan factions have stepped up their rhetoric against opponents in the west. The eastern camp has long been backed by Egypt and the UAE, while accusing Qatar of supporting Islamist-leaning rivals based in west Libya.

A statement issued on Sunday by the eastern government called for “immediate measures by all oil companies to stop any kind of dealing” with Glencore.

Days earlier, the eastern parliament said the NOC “had to review and cancel its contracts with some companies wholly or partly owned by the state of Qatar and the leaders of the global organization of the Muslim Brotherhood”.

Glencore, which since 2015 has been the only company able to buy Sarir and Messla crude output directly from the NOC, declined to comment.

NOC Chairman Mustafa Sanalla said he had warned the head of the eastern government, Abdullah al-Thinni, against any new port blockades.

“We respect the Libyan National Army General Command for its responsible opposition to port blockades,” Sanalla wrote, according to the NOC statement. “I hope you will take notice of their wise position on this matter.”

He said contracts signed by Naji al-Maghrabi, who Thinni appointed to head the parallel NOC, “were with companies NOC would not accept as counterparties, and could cost Libya billions of dollars in lost revenue if they were ever implemented”.

Maghrabi told Reuters that any contracts signed “were marketing contracts only”, and that the eastern government and NOC Benghazi were not demanding any halt to exports.

— CNBC’s Tom DiChristopher contributed to this story.