Gaddafi has attempted to put down protests with a violent crackdown, triggering some of the worst bloodshed in the two months since unrest began sweeping across the Arab world.

In the first sign of serious unrest in the capital, thousands of protesters clashed with supporters of Gadaffi in Tripoli. Gunfire could be heard and police using tear gas to disperse the demonstrators.

In Benghazi, centre of Libya's unrest, tens of thousands of people took to the streets and appeared to be in control of the city before security forces opened fire and killed scores.

Benghazi residents said soldiers from a unit had joined their protest and defeated a force Gaddafi's elite guards. Bodies were brought to a hospital riddled with bullets and wounds from rocket-propelled grenades.

A witness in Tripoli said police in the capital were using tear gas against protesters, some of whom were throwing stones at billboards of Gaddafi.

An expatriate worker said protesters were being dispersed by police and he could see burning cars in the capital.

The spread of unrest to Tripoli is a major development as protests so far, the biggest of Gaddafi's rule, were mostly confined to the east of the country where his grip is weaker.

In Benghazi, Habib al-Obaidi, head of the intensive care unit at the main Al-Jalae hospital, said the bodies of 50 people, mostly killed by gunshots, were brought there on February 20. The deaths came after scores were killed on February 19.