Libya's parliament has ordered a special force be sent within one week to "liberate" all rebel-held ports in the volatile east, officials said on Monday, raising the stakes over a blockage that has cut off vital oil revenues.

The rebels, which have seized three ports and partly control a fourth in the Opec member country, said they had dispatched forces to deal with any government attack.

The two sides seemed to be heading for military confrontation after a North Korean-flagged tanker finished loading crude worth $30 million at rebel-held Es Sider port despite a government threat to bomb the ship.

Western powers worry the North African country will slide deeper into chaos or even break apart as the government struggles to control militias who helped oust Muammar Gaddafi in 2011 but now defy state authority.

Parliament ordered the formation of a military force made up of regular soldiers and allied militias from across Libya to free the ports, which previously handled a total of more than 700,000 barrels of oil per day.

The operation will start within one week, parliament head Nuri Ali Abu Sahmain said in a decree published by spokesman Omar Hmeidan. "The force will be set up to liberate the ports and end the blockage," Hmeidan told Reuters.

Prime Minister Ali Zeidan, who said on Saturday the Morning Glory tanker would be bombed if it tried to export oil, is now in a much stronger position with the parliament throwing its weight behind military action.

Libya has been trying to rebuild its army since Gaddafi's overthrow, but analysts say it is not yet a match for battle-hardened militias that fought in the eight-month uprising that toppled him.

Still, the force will be drawn from cities such as Misrata that are home to fighters who saw battle in the civil war, according to the decree. Misrata forces were sent earlier this year to assist with clashes deep in Libya's south.

The rebels, made up of former oil security guards, said they had sent forces by land and sea to confront any government attackers.

"We have sent land forces to defend Cyrenaica to the west of Sirte ... and we also have boats patrolling regional waters," Essam al-Jahani, a member of the rebels' leadership team, told Reuters.

Cyrenaica is the historic name for eastern Libya, for which the rebels demand political autonomy and a share of oil revenues like under King Idris, who preceded Gaddafi.

Sirte, Gaddafi's birthplace, is a coastal city that forms a stronghold for Islamists and militias in central Libya.

TANKER STILL DOCKED

On Sunday, Tripoli said the navy and pro-government militias had sent boats to stop the tanker from leaving. The rebels said any attack on the vessel would be "a declaration of war".

The 37,000-tonne vessel was still docked on Monday afternoon at Es Sider, where it arrived on Saturday. State-run National Oil Corp (NOC) said it would sue anyone trying to buy the oil.

"NOC will ... enforce its rights over the cargo and hold responsible all the parties participating in illicit transactions relating to it in any jurisdiction, both within and outside of Libya," it said in a statement.

The conflict over oil wealth is increasing fears that Libya may slide deeper into chaos or even splinter as the fragile government fails to rein in the rebels.

The protesters are led by a former anti-Gaddafi commander, Ibrahim Jathran.

While the navy opened fire on a Maltese-flagged tanker trying to approach Es Sider in January, analysts say a full military confrontation with Jathran would be unlikely.

Jathran's campaign seeking more rights for Libya's underdeveloped east has won him sympathy, but many people dismiss him as a tribal warlord with no political vision.

Libya's top Islamic clerics urged militias who had helped topple Gaddafi to assist the government in trying to stop the tanker.

Tripoli has held indirect talks with Jathran, but fears his demand for a greater share of oil revenue for eastern Libya might lead to secession. - Reuters