Libyan leader Muammar Gadhafi fought an increasingly bloody battle to hang on to power on Monday when anti-government protests against his 41-year rule struck the capital Tripoli after days of violence in the east.
Various media sources have reported that more than 600 people have been killed since the unrest began last week.
Residents reported gunfire in parts of Tripoli on Monday and one political activist said warplanes had bombed the city.
Forces loyal to Gadhafi have killed hundreds of people across the country, human rights groups and witnesses said, prompting widespread condemnation from foreign governments
No independent verification of the reports was available and communications with Libya from outside were difficult.
But a picture emerged that suggested the survival of a leader who has loomed large on the world stage for decades and controls vast reserves of oil was in jeopardy.
"What we are witnessing today is unimaginable. Warplanes and helicopters are indiscriminately bombing one area after another. There are many, many dead," Tripoli resident Adel Mohamed Saleh said in a live broadcast on Al Jazeera television. "Anyone who moves, even if they are in their car they will hit you."
"We don't know what is going on, all we can hear are occasional gun shots," another Tripoli resident said.
Two Libyan fighter jets landed in Malta, their pilots defecting after they had been ordered to bomb protesters, Maltese government officials said. An analyst for London-based consultancy Control Risks said the reported air attacks indicated the end was near for Gadhafi.
"These really seem to be last, desperate acts. If you're bombing your own capital, it's really hard to see how you can survive," its Middle East anaylst Julien Barnes-Dacey said.
The demonstrations spread to the Mediterranean Sea capital after several cities in the east, including Benghazi, appeared to fall to the opposition, according to residents' accounts.
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".
The building where the General People's Congress, or parliament, meets in Tripoli was on fire on Monday, as was a police station in an eastern suburb, witnesses said.
Al Jazeera television quoted medical sources as saying 61 people had been killed in the latest protests in Tripoli; another source out the figure at 250.
Al Jazeera said security forces were looting banks and other government institutions in Tripoli, and protesters had broken into several police stations and ransacked them.
One of Gadhafi's sons said the veteran leader would fight the revolt until "the last man standing". But a coalition of Libyan religious leaders told all Muslims it was their duty to rebel against the Libyan leadership because of its "bloody crimes against humanity".
Some analysts suggested Libya 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 Center in Qatar.
"I think what's going to happen is going to be much more chaotic than what we saw in Egypt or Tunisia. Gaddafi and his sons don't have anywhere else to go...They are going to fight," said North Africa analyst Geoff Porter, contributor to political risk consultancy Wikistrat.
Output at one of Libya'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 Libya'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 said on its website on Monday.
At least nine towns in the east were under the control of protesters loyal to tribal groups, the president of the International Federation for Human Rights in France said.
Support for Gaddafi, who seized power in 1969, among Libya's desert tribes was also waning. The leader of the Al-Zuwayya tribe in the east threatened to cut oil exports unless authorities halted "oppression of protesters".
Libya is Africa's fourth biggest oil exporter, producing 1.6 million barrels a day. The oil price jumped $3 to $89.50 a barrel for U.S. crude on fear the unrest could disrupt supplies.
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. The ambassadors to China and the Arab League made similar declarations.
Libya's deputy prime minister and sources in Caracas, meanwhile, denied reports that Gaddafi had fled to Venezuela - ruled by his friend and fellow revolutionary President Hugo Chavez.
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