Fears of a fracturing of Libya's opposition heightened after units loyal to the ruling National Transitional Council stormed the base of what it said was a renegade unit in the rebel capital, Benghazi.
Four fighters were killed and six wounded in the attack on the al-Nidaa Brigade, blamed for Thursday's assassination of army commander Abdel Fatah Younis.
NTC spokesman Mahmoud Shammam said the attack was ordered two days after the brigade, which officials claim is Islamist, attacked two Benghazi jails, freeing more than 200 inmates. "We consider them members of the fifth column,."
One unverified rumour in Benghazi is that the al-Nidaa brigade received secret coded orders communicated through an announcer, Yusef Shakir, on Muammar Gaddafi's state television. Three state TV transmitters were bombed by Nato on Saturday night. Gaddafi's regime claimed three journalists were killed and a further 15 people wounded.
"We're not a military target," said government spokesman Khalid Bazelya. "We are not commanders in the army, and we do not pose a threat to civilians."
However, in London the Ministry of Defence defended the attack on the transmitters. A spokesman said: "This strike was an attempt to disrupt the broadcast of Gaddafi's murderous rhetoric, which has repeatedly sought to incite violence against fellow Libyans."
Outwardly, foreign backers of the rebels insist the NTC is sound, with French defence minister Gerard Longuet saying Paris was not pushing for an immediate resolution: "Impatience is never a good adviser." He insisted an end to the conflict rested with the people of the Libyan capital: "Things have to move in Tripoli. To put it clearly, the population has to rise up."
Nerves remain frayed in Benghazi and questions remain over the role, if any, of NTC officials in the death of Younis, following an admission that he had been arrested for questioning on treason allegations just hours before his death.
In London, the defence secretary, Liam Fox, would not be drawn on the assassination. "It's not yet clear who carried out the killing, and there are claims and counter-claims," he said. "It will be at least several days until we know exactly what the situation was. There has always been a mixture of people who make up the opposition forces – hardly surprising given the country's history – and it would be for the Libyans themselves to sort out exactly how any power structure develops post-Gaddafi."
Sir Menzies Campbell, former leader of the Liberal Democrats, said the killing raised questions about the stability of the NTC and demonstrated the need for a "wholesale" review of policy. He told Sky News: "The assassination has thrown into fairly sharp focus the whole question of the Transitional National Council. What kind of government [it would be], for example, [if] it ever got to Tripoli.
"I also think that claims of success have always got to be taken with a certain amount of scepticism because it's not about just taking ground temporarily, its taking it permanently. I've been saying I think we should take this period for a wholesale examination of policy.
"I supported the military action – I continue to support the British government's involvement – but I think we have to have a pretty clearer view about what the NTC would be like were they ever to get to Tripoli."
In stark contrast to the uncertainty in Benghazi, rebel forces in both Misrata and the Nafusa mountains reported significant breakthroughs against government forces.
West of the besieged city of Misrata, rebel units aided by intensive Nato bombing broke through the frontline in several places, advanced nine miles and captured abandoned tanks, artillery and truck-mounted grad rocket launchers near the town of Zlitan.
Four of the huge 155mm guns were seen by the Guardian being hauled by trucks from the frontline late on Saturday night. Fierce fighting for Zlitan continued on Sunday, bringing the death toll of rebel fighters over the weekend to 23, with more than 100 wounded and three civilians killed in shelling of Misrata city.
Rebel commanders claim that government forces appear to be disintegrating in many sectors."The resistance today was not that much. I don't know, maybe he doesn't have an army," said Mohammed Elfituri of the Faisal (Sword) Brigade. "We thought that it would be hard work [but] we moved 15 kilometres." Similar gains were reported by rebel units pushing north from bases in the Nafusa mountains, who say they have captured one town, Hawamid, and surrounded a second, Tiji, 150 miles south west of Tripoli.
