Libyan officials say government forces have seized a tanker loaded with crude oil that a separatist militia was attempting to export in defiance of the country's central authorities.
Military and oil industry sources said Monday that the Libyan navy had intercepted the ship as it attempted to leave the eastern port of As-Sidra and was leading it "to a port controlled by the state."
A rebel spokesman had earlier denied they had lost control of the ship.
The vessel - Morning Glory - is North Korea-flagged, but it is not clear who actually owns it. Shipping sources say it is a flag of convenience to keep ownership secret.
Also Monday, Libya's parliament ordered special forces to deploy within a week to "liberate" all rebel-held ports in the country's volatile east.
The head of parliament, Nuri Ali Abu Sahmain, who has quasi-presidential powers, ordered the formation of a force made up of regular soldiers and allied militias to take back the ports, which previously handled a total of more than 700,000 barrels of oil per day.
As-Sidra and Libya's other major ports have been under militia control for the last eight months, slowing the country's oil output to a trickle.
Morning Glory finished loading crude worth $30 million on Sunday, bypassing Tripoli authorities despite a government threat to bomb it should it sail away. Armed gunmen forced workers loyal to the government to dock the ship Saturday.
The United States earlier warned of consequences related to any unauthorized sales of crude oil loaded onto the vessel.
The oil belongs to Libya's National Oil Corporation and its three U.S. consortium partners. Libya has banned militias from selling crude directly to the world market.
Prime Minister Ali Zeidan warned that Libya will hold responsible the tanker's captain, owner and the country under which the flag sails for what he called a "criminal act."
Analysts say the Libyan military would likely struggle to overcome rebels battle-hardened in the 2011 uprising that toppled Moammar Gadhafi. The rebels have kept their weapons and now challenge state authority.
The oil dispute is just one facet of the deepening turmoil in the North African OPEC-member nation.
Bringing Libya's factions and heavily-armed militias together under one flag continues to pose a great challenge. Analysts say the consequences of failure would affect the entire region.