The death toll from four days of violence centred on the Libyan city of Benghazi has passed 100, Human Rights Watch said on Sunday, after witnesses said security forces shot dozens more anti-government protesters.

The unrest, the worst in Libyan leader Muammar Gaddafi's four decades in power, started out as a series of protests inspired by popular revolts in neighbouring Egypt and Tunisia but was met by a fierce security crackdown.

Witnesses in the eastern city of Benghazi said security forces had pulled back to a fortified compound in the centre of the town from where they were shooting at people returning from burying protesters killed on previous days.

"Dozens were killed ... We are in the midst of a massacre here," a witness told Reuters. The man said he had helped take victims to hospital in Benghazi.

New York-based Human Rights Watch said it had raised its death toll from the previous 84 to 104, after at least 20 more people were killed in Benghazi on Saturday.

It said that death toll, compiled from interviews with witnesses and hospital officials, was "conservative." The Libyan government has not released any casualty figures or made any official comment on the violence.

A Benghazi hospital doctor said victims had suffered severe wounds from high-velocity rifles.

The bloody crackdown prompted about 50 Libyan Muslim religious leaders to issue an appeal, sent to Reuters, for the security forces, as Muslims, to stop the killing.

"This is an urgent appeal from religious scholars (faqihs and Sufi sheikhs), intellectuals, and clan elders from Tripoli, Bani Walid, Zintan, Jadu, Msalata, Misrata, Zawiah, and other towns and villages of the western area," said the appeal.

"We appeal to every Muslim, within the regime or assisting it in any way, to recognize that the killing of innocent human beings is forbidden by our Creator and by His beloved Prophet of Compassion (peace be upon him)... Do NOT kill your brothers and sisters. STOP the massacre NOW!"

Benghazi and the surrounding area have been the focus of the unrest, but posts on social network sites, which could not be verified, referred to minor clashes in the capital Tripoli and of overnight gunfire in Nalut, to the west.

Libya watchers say an Egypt-style nationwide revolt is unlikely because Gaddafi has oil cash to smooth over social problems, and is still respected in much of the country.

Gaddafi has traditionally had less support in the eastern region around Benghazi than in the rest of the oil-producing country, and the city has been the scene of violence in the past.

"Gaddafi will find it hard to make concessions in order to survive. I think the attitude of the Libyan regime is that it's all or nothing," Sir Richard Dalton, a former British ambassador to Libya, told the Independent on Sunday newspaper.

Witness accounts have been hard to verify independently because Libyan authorities have not allowed foreign journalists into the country since the protests erupted and local reporters have been barred from travelling to Benghazi.

Mobile phone connections have often been out of service and Internet service in Libya has been cut off, according to a U.S. company that monitors web traffic. People in Tripoli said they had Internet access late on Saturday.

BENGHAZI "LIBERATED"

A Benghazi resident said security forces were confined to a compound from which snipers were firing at protesters.

"Right now, the only military presence in Benghazi is confined to the Command Centre Complex in the city. The rest of the city is liberated," he said late on Saturday.

"Thousands and thousands of people have gathered in front of Benghazi's court house ... All the revolutionary committee (local government) offices and police stations in the city have been burned," he said.

The private Quryna newspaper, which is based in Benghazi and has been linked to one of Gaddafi's sons, said 24 people were killed in Benghazi on Friday. It said security forces fired to stop protesters attacking the police headquarters and a military base where weapons were stored.

"The guards were forced to use bullets," the paper said.

In Green Square in the centre of Tripoli, next to the walled old city, several hundred people gathered on Saturday, waving portraits of Gaddafi and chanting "Our revolutionary leader!" and "We follow your path", a Reuters reporter said.

A state-controlled newspaper said the Benghazi violence was part of "the dirty plans and the conspiracies designed by America and Zionism and the traitors of the West".