TRIPOLI, Jan 6 (Reuters) - The Libyan navy has prevented an oil tanker from loading crude at the eastern port of Es-Sider which has been seized by protesters, state-run National Oil Corp (NOC) said on Monday.
"The Libyan navy....dealt on Sunday with a Malta-flagged tanker which tried entering es-Sider port in cooperation with an illegal group to load and smuggle crude oil," NOC said in a statement.
A group seeking autonomy for eastern Libya seized the port and two others last year to demand a greater share of Libya's oil wealth. It has repeatedly said it might sell crude on its own, bypassing the central government, but there had been no sign so far it had contracted foreign buyers.
The group, based in Ajdabiya in the east, was not immediately available for comment.
NOC did not say whether any military force had been used, saying only: "The Libyan navy prevented the tanker from reaching Es-Sider."
Libya had warned the owner of the ship that approaching the port had been illegal and warned it would stop any tanker trying "to smuggle and steal Libyan oil illegally."
The heavily-armed group calling for autonomy and a greater share of oil sales is occupying the eastern Ras Lanuf, Es-Sider and Zuweitina ports, which previously accounted for 600,000 barrels a day of oil exports.
NOC extended on Saturday force majeure for the ports, a legal term to cover the suspension of contract obligations.
Prime Minister Ali Zeidan said last month tribal elders would hold more talks with the group led by Ibrahim Jathran, a hero from the 2011 uprising which toppled Muammar Gaddafi, but there has been so sign of any progress.
Western powers fear the North African country will slide into instability as the government struggles to rein in militias that helped topple Gaddafi but kept their arms.
Zeidan has said the government will act against the oil strikes but Libya's nascent army, still in training, is too weak to tackle armed protesters, analysts say. (Reporting by Ulf Laessing, Ghaith Shennib and Patrick Markey, editing by William Hardy)