Tripoli - Libyan leader Muammar Gaddafi's four-decade-old rule appeared in increasing jeopardy on Monday as anti-government protests reached the capital for the first time, leaving dozens dead at the hands of the security forces.
Several cities in the east appeared to be in the hands of the opposition as protests spread from Benghazi, cradle of a popular uprising that has rattled one of the Arab world's most entrenched governments.
One of Gaddafi's sons said the veteran leader would fight the revolt until "the last man standing."
Protesters rallied in Tripoli's streets, tribal and religious leaders spoke out against Gaddafi, and army units defected to the opposition in a revolt that has cost the lives of more than 200 people.
Protesters said they had taken control of Benghazi and other cities, with some analysts suggesting the country was heading for civil war.
"Libya is the most likely candidate for civil war because the government has lost control over part of its own territory," said Shadi Hamid, director of research at the Brookings Doha Centre in Qatar.
Output at one of the country's oil fields was reported to have been stopped by a workers' strike and some European oil companies withdrew expatriate workers and suspended operations. Most of the country's oil fields are in the east, south of Benghazi.
Anti-government protests have also broken out in the central town of Ras Lanuf, the site of an oil refinery and petrochemical complex, Libya's Quryna newspaper reported on its Internet site on Monday.
In signs of disagreement inside Libya's ruling elite, the justice minister resigned in protest at the "excessive use of violence" against protesters.
In India, Libya's ambassador said he was resigning in protest at the violent crackdown.
A coalition of Libyan Muslim leaders told all Muslims it was their duty to rebel against the Libyan leadership because of its "bloody crimes against humanity."
European nations watched developments in Libya with a growing sense of alarm after the government in Tripoli said it would suspend cooperation on stemming the flow of illegal immigrants across the Mediterranean.
Prime Minister David Cameron, on a visit to the region, said events in Libya were appalling and unacceptable.
Al Jazeera television quoted medical sources as saying 61 people had been killed in the latest protests in Tripoli.
It said security forces were looting banks and other government institutions in Tripoli, and protesters had broken into several police stations and wrecked them.
A Reuters reporter in Tripoli said residents were stocking up on essential goods, apparently in anticipation of new clashes after nightfall. There were long queues at food shops and long lines of cars at fuel stations.