Libya''s Muammar Gaddafi will fight a popular revolt to "the last man standing", one of his sons said on Monday, after protests broke out in the capital for the first time following days of unrest in the city of Benghazi.

Anti-government protesters rallied in Tripoli''s streets, tribal leaders spoke out against Gaddafi, and army units defected to the opposition as oil exporter Libya endured one of the bloodiest revolts to convulse the Arab world.

Gaddafi''s son Saif al-Islam Gaddafi appeared on national television in an attempt both to threaten and calm people, saying the army would enforce security at any price.

"Our spirits are high and the leader Muammar Gaddafi is leading the battle in Tripoli, and we are behind him as is the Libyan army," he said.

"We will keep fighting until the last man standing, even to the last woman standing ... We will not leave Libya to the Italians or the Turks."

Wagging a finger at the camera, he blamed Libyan exiles for fomenting the violence. But he also promised dialogue on reforms and wage rises.

The cajoling may not 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.

"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 Benghazi told the BBC after watching the speech.

"He is liar, liar, 42 years we have heard these lies."

The United States said it was weighing "all appropriate actions" in response to the unrest.

"We are analysing the speech ... to see what possibilities it contains for meaningful reform," a U.S. official said.&' || 'nbsp; Libya''s ambassador to India told the BBC he was resigning in protest at the violent crackdown that has killed more than 200.

Ali al-Essawi also accused the government of deploying foreign mercenaries against the protesters.

In the coastal 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.

"Security now it is by the people" the lawyer said.&' || 'nbsp; In the first sign of serious unrest in the capital, thousands of protesters clashed with Gaddafi supporters. Gunfire rang out in the night and police used tear gas to disperse demonstrators, some of whom threw stones at Gaddafi billboards.

South Korea said hundreds of Libyans, some armed with knives and guns, attacked a South Korean-run construction site in Tripoli, injuring at least 4 foreign workers.

Human Rights Watch said at least 223 people have been killed in five days of violence. Most were in Benghazi, cradle of the uprising and a region where Gaddafi''s grip has always been weaker than elsewhere in the oil-rich 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.

"One of the victims was obliterated after being hit by an RPG (rocket-propelled grenade) to the abdomen," 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.

"They are now saying that they have overpowered the Praetorian Guard and that they have joined the people''s revolt," another man at the hospital, lawyer Mohamed al-Mana, told Reuters by telephone.