Libya says government forces have intercepted a North Korean-flagged oil tanker which had loaded crude from a rebel-held eastern port.

Prime Minister Ali Zeidan said on Monday the forces took over the oil tanker but it has not yet reached a port controlled by the state, Reuters reported.

"The ship is around 20 miles from Es Sider," Zeidan said, adding, "It stopped due to darkness and won't move tonight but is under complete control and secured. Tomorrow it will move."

Authorities would unload the crude from the tanker once it reaches a western port and then launch legal measures against the potential buyers.

Zeidan also vowed Libya would end the blockade of all rebel-held ports in the east either through talks or by military force.

"What is confirmed it that all ports will be liberated from the occupiers with all means possible," he said. "We prefer talks but if talks fail then the state will act," he stated.

On Sunday, militants warned the government against harming the tanker, saying such a move would be a “declaration of war.”

The ship, the Morning Glory, started loading at the Es Sider port on Saturday despite earlier threats by the Libyan government to bomb the ship.

The incident involving the tanker marks the easterners’ first attempt to sell oil.

Tripoli has made efforts to end a wave of protests at oil ports and fields across the country that have drastically reduced its oil output.

Libya has been witnessing numerous clashes between government forces and rival militia groups, who played a key role in the 2011 popular uprising that toppled former dictator Muammar Gaddafi.

Since August 2013, the rebels have managed to seize three major Libyan ports.

The rebels refuse to lay down arms despite efforts by the central government to impose law and order.

During a conference held in the Italian capital Rome on Thursday, senior officials from over 40 countries said that the ongoing tensions in Libya could slip out of control if a political solution was not found.

"The situation in Libya is very worrying," French Foreign Minister Laurent Fabius told reporters on the sidelines of the second Ministerial Conference on International Support to Libya.