Libya faces civil war and "rivers of blood", the son of its leader Muammar Gaddafi warned on Monday, as a brutal crackdown failed to stop an unprecedented popular uprising from reaching the capital.
With gunfire crackling in the streets of Tripoli, and Human Rights Watch putting the death toll at 233 since Thursday, Saif Al-Islam Gaddafi vaguely promised reforms as he condemned the revolt as a foreign plot.
"Libya is at a crossroads. If we do not agree today on reforms .... rivers of blood will run through Libya," he said in a fiery but rambling televised speech that betrayed a note of desperation within his father's 41-year regime.
"We will take up arms... we will fight to the last bullet," he said. "We will destroy seditious elements. If everybody is armed, it is civil war, we will kill each other.
"Libya is not Egypt, it is not Tunisia," added Saif Al-Islam Gaddafi, 38, who has no defined political role but wields vast influence.
The elder and famously mercurial Gaddafi, 68, the longest-serving leader in the Arab world, and whose nation holds Africa's biggest oil reserves, remained out of sight.
Heavy gunfire broke out in central Tripoli and several city areas on Monday for the first time since the uprising began in eastern Libya, witnesses and an AFP journalist reported.
Several witnesses said fire was set to public buildings overnight, including the state broadcasting offices and branches of the People's Committees that are the mainstay of the regime.
Some 500 Libyans meanwhile stormed and looted a South Korean construction site near the capital on Monday, injuring about 15 Bangladeshi as well as three South Korean workers, Seoul's foreign ministry said.
Earlier, witnesses reported clashes in Tripoli's downtown Green Square between protesters and Gaddafi supporters, and a witness in the working-class Gurgi area reported that security forces had fired tear gas at protesters.
In London, British energy giant BP said it was preparing to evacuate some of its staff.
In Brussels, Spain's Foreign Minister Trinidad Jimenez said the 27-nation European Union was "coordinating the possible evacuation of EU citizens coming from Libya, especially from Benghazi."
In Cairo, where up to 400 protesters went to the Libyan embassy on Sunday chanting for the fall of Gaddafi's regime, Libya's envoy to the Arab League said he had resigned to "join the revolution."
The Libyan ambassador to India, Ali Al-Issawi, also resigned in an interview with the BBC to protest against the regime's "use of violence against its citizens" and deployment of "foreign mercenaries against Libyans."
A third Libyan diplomat, in Beijing, quit as well, saying that Gaddafi may have fled the country and that a "gunfight' had taken place between his sons, Al-Jazeera television reported.
The unrest in Libya has spread from the flashpoint second city of Benghazi, where demonstrations flared on Tuesday, to the Mediterranean town of Misrata, just 200 kilometres (120 miles) from Tripoli.
"Lawyers are demonstrating outside the Northern Benghazi court; there are thousands here. We have called it Tahrir Square Two," a lawyer there said, alluding to the Cairo epicentre of protests that brought down Egypt's Hosni Mubarak.
Winesses told AFP by telephone that in Misrata, security forces backed by "African mercenaries" had fired on crowds "without discrimination."
Saif Al-Islam Gaddafi himself suggested that Benghazi, long an opposition hotbed, was out of government control.
"At this moment there are tanks being driven by civilians in Benghazi," he said, insisting the uprising was aimed at installing Islamist rule and that it would be ruthlessly crushed.
Separately, Prime Minister Baghdadi Mahmudi told EU ambassadors in Tripoli on Sunday that there are "very precise plans, destructive and terrorist, that want Libya to become a base for terrorism."
Underscoring Libya's vast oil wealth, the younger Gaddafi said: "We have one resource that we live on and that is petrol. All the foreign companies will be forced to leave the country.
"This is an opposition movement, a separatist movement which threatens the unity of Libya," the besuited Gaddafi said in a fiery but rambling speech which blamed Arab and African elements for fomenting the troubles.
The United States and the European Union strongly condemned the use of lethal force, while UN Secretary General Ban Ki-moon called for "the non-use of force and respect for basic freedoms".