Russian envoy Mikhail Margelov was headed for Tripoli on Thursday seeking to mediate in Libya's conflict, as rebels made gains in the west and Nato insisted it needs no ground troops to back its mission.

Margelov, the Africa envoy of Russian President Dmitry Medvedev, left Moscow for Tunisia on Wednesday evening, from where he will travel to the Libyan capital by car on Thursday, his spokeswoman Varvara Paal told AFP in Moscow.

During his visit, which will last only a day, he will meet the Prime Minister and foreign minister, but was not scheduled to meet Libyan strongman Muammar Gaddafi.

Margelov, a senior lawmaker and the Kremlin’s representative to Africa, said in May it was becoming increasingly difficult to hold talks with Gaddafi.

Last week, Margelov travelled to the Libyan rebel stronghold of Benghazi and Cairo where he held talks with Gaddafi’s cousin Ahmed Gaddaf al-Dam and other people from his circle.

He said at that time that after his visit to Tripoli, Moscow would be prepared to offer a preliminary “roadmap” for settling the conflict.

Anti-Gaddafi rebels, meanwhile, seized three villages as they sought control of a key junction connecting the towns of Yafran and Zintan, west of Tripoli, an AFP correspondent reported.

Rebels were seen patrolling the streets of Zawit Bagoul, 20 kilometres (12.5 miles) from Zintan. Pro-Gaddafi positions on the outskirts of Zawit Bagoul were deserted and loyalists left behind clothes, shoes and ammunition.

The correspondent said the rebels later also moved into Lawania, about seven kilometres away, and then Ghanymma, less than 10 kilometres from Yafran, as Nato aircraft were heard overhead.

Libyan authorities organised a visit on Wednesday for Tripoli-based foreign journalists to Gharyan, 100 kilometres south of the capital and 30 kilometres from hotly-disputed Yafran, to show the situation in the town was calm.

Anti-regime graffiti on the walls had been painted over and activity in Gharyan appeared normal.

Nato, which has carried out 10 weeks of air strikes against Gaddafi’s forces, can see out its mission without ground troops, its operations commander said in a briefing on an Italian aircraft carrier.

Lieutenant General Charles Bouchard also said that the military situation in western Libya, where there has been an upsurge in fighting between regime loyalists and rebel forces, was developing “very positively.”

“I do believe we can complete the mission without bringing in ground troops,” the Canadian general told reporters off Libyan shores on the Garibaldi. “We are receiving adequate assets to complete the mission and carry out our mandate.”

Senior military officials from Britain and France, key players in the Nato campaign, have expressed concerns about how to maintain the Nato operation, which has been extended for a second three-month period from June 27.

Libyan state television said that a Nato strike on a bus in the town of Kikla, near Yafran, on Wednesday had killed 12 of its passengers.

Nato on Thursday denied the claim.

“Nato did not conduct any air strike in the city on Wednesday,” a senior official in the alliance told AFP on condition of anonymity.

Ahead of talks with Nato secretary general Anders Fogh Rasmussen, British Prime Minister David Cameron insisted that Britain could sustain its Libya operation long-term, after its navy chief warned of tough choices if the campaign lasts more than six months.

The premier said he had met First Sea Lord Admiral Mark Stanhope, the head of the Royal Navy, following his comments.

"I had a meeting with the first sea lord yesterday and he agreed that we can sustain this mission for as long as we need to," he said.

In Washington, a bipartisan group of US lawmakers sought to throw a roadblock in front of President Barack Obama's Libya policy, filing a lawsuit that charges that US military operations are unconstitutional.

Anti-war Democratic Representative Dennis Kucinich and nine other members of the House signed the lawsuit challenging the Obama administration's circumvention of Congress in authorising use of military force in a protracted campaign.

"With regard to the war in Libya, we believe that the law was violated. We have asked the courts to move to protect the American people from the results of these illegal policies," Kucinich said.

The White House later delivered a report to Congress that it said justifies its role in the Libya conflict and insisting that Obama did not exceed his powers in ordering the action.

Officials said the 30-page report details the US role in the mission to protect civilians and attack Gaddafi’s forces and contained a detailed legal analysis showing the action is permitted under US law.