The 40-year rule of Col Muammar Gaddafi is under threat amid spiralling unrest throughout Libya.
Several senior officials - including the justice minister - have reportedly resigned after security forces fired on protesters in Tripoli overnight.
Witnesses say renewed protests have hit two suburbs of the capital.
In an earlier TV address, Col Gaddafi's son Saif al-Islam conceded that the eastern cities of al-Bayda and Benghazi were under opposition control.
But he warned of civil war and vowed that the regime would "fight to the last bullet".
The BBC's Jon Leyne, in neighbouring Egypt, says Col Gaddafi has now lost the support of almost every section of society.
Reliable sources say Col Gaddafi has now left the capital, our correspondent adds.
'Hatred of Libya'
After clashes in the capital overnight were suppressed by security forces, state TV reported a renewed operation had begun against opposition elements there.
"Security forces have started to storm into the dens of terror and sabotage, spurred by the hatred of Libya," the Libyan TV channel reported.
An eyewitness in Tripoli told the BBC that the suburbs of Fashloom and Zawiyat al-Dahmani had been cordoned off by security forces.
Protesters were out on the streets and flames and smoke could be seen rising from the area, the witness said.
Amid the turmoil on the streets, senior officials have also begun to desert the regime.
Justice Minister Mustapha Abdul Jalil quit the government because of the "excessive use of violence", the privately owned Quryna newspaper reported.
In New York, Libya's deputy ambassador to the UN denounced the Gaddafi government, accusing it of carrying out genocide against the people.
Libya's envoy to the Arab League, Abdel Moneim al-Honi, announced he was "joining the revolution", and its ambassador to India, Ali al-Essawi, told the BBC he was also resigning.
In another blow to Col Gaddafi's rule, two tribes - including Libya's largest tribe, the Warfla - have backed the protesters.
Meanwhile, two helicopters and two fighter jets from Libya landed in Malta.
The helicopter was said to be carrying French oil workers.
The fighter pilots, both colonels, took off from a base near Tripoli after they had been ordered to bomb protesters, Maltese officials quoted by Reuters news agency said.
The agency said one of them had asked for asylum.
Human Rights Watch says at least 233 people have died since last Thursday, though in his speech, Saif al-Islam insisted reports of the death toll had been exaggerated.
The US, UK and French governments are among those condemning the harsh treatment of protesters.
The US has ordered all families of embassy staff and all non-essential diplomats to leave the country.
Italy, the former colonial power in Libya, has close business links to Tripoli and voiced alarm at the prospect of the Gaddafi government collapsing.
"Would you imagine to have an Islamic Arab Emirate at the borders of Europe? This would be a very serious threat," said Foreign Minister Franco Frattini.
The head of the Arab League, Amr Moussa, described the protesters' demands as legitimate, calling it a "decisive moment in history" for Arab nations.
Oil price jumps
Reports from several cities suggest the country is sliding out of the government's control:
- In Az-Zawiya, 40km (25 miles) west of Tripoli, witnesses say the police have fled, government buildings have been burnt down and the city is in chaos.
- Unconfirmed reports from the port city of Darnah say protesters are holding more than 300 workers hostage - many of them Bangladeshis.
- Several hundred Libyans stormed a South Korean-run construction site west of Tripoli, injuring at least four workers.
- In Benghazi, reports say 11 solders were killed by their commanding officers for refusing to fire on protesters.
The violence has helped to push up oil prices to their highest levels since the global financial crisis of 2008.
At one point, Brent crude - one of the main benchmarks on world oil markets - reached $105 (£65) a barrel.
International firms including BP, one of the world's biggest oil companies, are preparing to pull their staff out of Libya.