Dozens of people were reported killed in Tripoli overnight as anti-government protests reached the Libyan capital for the first time and the building where the country's parliament meets was ablaze.
One of Muammar Gaddafi's sons said the veteran leader would fight the popular revolt that has shaken his 40-year rule until "the last man standing".
Anti-government protesters rallied in Tripoli's streets, tribal leaders spoke out against Gaddafi, and army units defected to the opposition in a revolt that has cost the lives of more than 200 people. Protesters said they had taken control of two other cities.
Output at one of the country's oil fields was reported to have been stopped by a workers' strike and some European oil companies withdrew expatriate workers and suspended operations.
Anti-government protests have also broken out in the central town of Ras Lanuf, the site of an oil refinery and petrochemical complex, Libya's Quryna newspaper reported on its Internet site on Monday. The town is in Sirte, Gaddafi's home region.
With autocratic governments already toppled by popular uprisings in Tunisia and Egypt, there was a sense that Gaddafi's iron grip was being severely tested.
"Libya is the most likely candidate for civil war because the government has lost control over part of its own territory," said Shadi Hamid, director of research at the Brookings Doha Centre in Qatar.
Al Jazeera television quoted medical sources as saying 61 people had been killed in the latest protests in Tripoli.
It said security forces were looting banks and other government institutions in Tripoli, and protesters had broken into several police stations and wrecked them.
A Reuters reporter in Tripoli said residents were stocking up on essential goods, apparently in anticipation of new clashes after nightfall. He said there were long queues at food shops and long lines of cars at fuel stations.
The building where the General People's Congress, or parliament, meets when it is in session in Tripoli was on fire on Monday morning.
Gaddafi's son Saif al-Islam Gaddafi appeared on national television in an attempt both to threaten and to calm people, saying the army would enforce security at any price to put down one of the bloodiest revolts to convulse the Arab world.
"We will keep fighting until the last man standing, even to the last woman standing," he said on Sunday.
Wagging a finger at the camera, he accused Libyan exiles of fomenting the violence. But he also promised dialogue on reforms and wage rises.
But people in Tripoli expressed anger at the speech.
"I am sorry because I spent too much time last night waiting for the speech and then finally the speech disappointed me. I was expecting to hear something that calmed down the anger but instead it made the young people more angry," said a Tripoli resident who did not want to be identified.
Another man said: "We were waiting for something good for us, the young people, to calm the anger but he did nothing."
In an indication of disagreement inside Libya's ruling elite, Mohamed Bayou -- who until a month ago was chief government spokesman -- said the leadership was wrong to threaten violence against its opponents.
Bayou called on Saif al-Islam Gaddafi to start talks with the opposition.
"Gaddafi supporters in Tripoli's Green Square"
Gaddafi supporters were in central Tripoli's Green Square on Monday, waving flags and carrying his portrait, a Reuters reporter said.
At the Bab El Aziziya complex in the city, where Gaddafi has his residence and offices, soldiers stood guard as usual.
Saif al-Islam's cajoling is unlikely to be enough to douse the anger unleashed after four decades of rule by Gaddafi -- mirroring events in Egypt where a popular revolt overthrew the seemingly impregnable President Hosni Mubarak 10 days ago.
In the eastern city of Benghazi, protesters appeared to be largely in control after forcing troops and police to retreat to a compound. Government buildings were set ablaze and ransacked.
"People here in Benghazi are laughing at what he is saying. It is the same old story (on promised reform) and nobody believes what he says," a lawyer in Libya's second city told the BBC after watching Saif al-Islam's speech.
"Youths with weapons are in charge of the city. There are no security forces anywhere," University of Benghazi professor Hanaa Elgallal told Al Jazeera International television.
Salahuddin Abdullah, a self-described protest organiser, said: "In Benghazi there is celebration and euphoria ... The city is no longer under military control. It is completely under demonstrators' control."
In Al Bayda, a town about 200 km (125 miles) from Benghazi, which was the scene of deadly clashes last week between protesters and security forces, a resident told Reuters protesters were also in command.
European Union foreign ministers will condemn the repression in Libya at their meeting later on Monday, according to the draft of a joint statement.
The United States said it was weighing "all appropriate actions" in response to the unrest.
Human Rights Watch said at least 223 people had been killed in five days of violence. Most were in Benghazi, a region where Gaddafi's grip has always been weaker than elsewhere in the oil-producing desert nation.
Habib al-Obaidi, a surgeon at the Al-Jalae hospital, said the bodies of 50 people, most of them shot, were brought there on Sunday afternoon. Two hundred wounded had arrived, he said.
Members of an army unit known as the "Thunderbolt" squad had brought wounded comrades to the hospital, he said. The soldiers said they had defected to the cause of the protesters and had fought and defeated Gaddafi's elite guards.
The Libyan uprising is one of a series of revolts that have raced like wildfire across the Arab world since December, toppling the long-time rulers of Tunisia and Egypt and threatening entrenched dynasties from Bahrain to Yemen.
Support for Gaddafi, the son of a herdsman who seized power in 1969, among Libya's desert tribes was also waning. The leader of the Al-Zuwayya tribe in the east threatened to cut oil exports unless authorities halted "oppression of protesters".
Libya is Africa's fourth biggest oil exporter, producing 1.6 million barrels a day. The oil price jumped $3 to $89.50 a barrel for U.S. crude on fear the unrest could disrupt supplies.
A strike at Libya's Nafoora oilfield was reported to have stopped production, according to Al Jazeera television. BP suspended operations for oil and gas drilling.
AgenciesGüncelleme Tarihi: 21 Şubat 2011, 16:16