Col Muammar Gaddafi's regime is under pressure amid unprecedented protests in the Libyan capital and defections by senior diplomats.
Security forces fired live ammunition and tear gas on protesters in the streets of Tripoli late on Sunday.
Benghazi, the country's second city, now appears to be largely under the control of protesters.
But Col Gaddafi's son, Saif al-Islam, has warned that civil war could ignite.
In a lengthy TV address, he offered political reforms but also vowed that the regime would "fight to the last bullet" against "seditious elements".
He acknowledged, though, that the eastern cities of Benghazi and al-Bayda had fallen to the opposition.
Justice Minister Mustapha Abdul Jalil has become the latest senior official to resign. He said he was leaving his post because of the "excessive use of violence", privately owned Quryna newspaper reported on Monday afternoon.
'Massacre'
On Monday, reports from Tripoli suggested the streets were mainly quiet, with government forces still patrolling Green Square after crushing protests in what witnesses called a "massacre".
It followed a night of violence between supporters of Col Gaddafi and anti-government protesters.
Gunfire was heard into the early hours of the morning and firefighters struggled to contain a fire at a central government building, the People's Hall, which was earlier set ablaze.
In addition to the justice minister, several top government officials have quit over the violent crackdown.
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.
Mohamed Bayou, who until a month ago was chief spokesman for the Libyan government, said the leadership was wrong to threaten violence against its opponents.
Mr Bayou, in a statement quoted by the Reuters news agency, called on Saif al-Islam to acknowledge the opposition and open dialogue with them.
In another blow to Col Gaddafi's rule, two tribes - including Libya's largest tribe, the Warfla - have backed the protesters.
More violence ahead?
The BBC's Jon Leyne, in neighbouring Egypt, says it is beginning to look like a matter of time before Col Gaddafi's rule finally collapses.
However, Libyans are worried about how much more violence lies in store in the days ahead, he adds.
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 that have condemned the harsh treatment of protesters.
But Italy, the former colonial power in Libya, has close business links to Tripoli and voiced alarm at the prospect of the Gaddafi government collapse.
"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.
However, 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 in turmoil:
* 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.
source : bbc.co.uk
