Libyan leader Muammar Gaddafi's four-decade-old rule appeared in increasing jeopardy on Monday when days of anti-government protests reached the capital for the first time and security forces killed dozens of people.

Military aircraft fired live ammunition at crowds of anti-government protesters in the capital Tripoli, Al Jazeera television said on Monday quoting witnesses. No independent verification of the report was immediately available.

Residents said several cities in the east appeared to be in the hands of the opposition as protests spread from Benghazi, the cradle of a popular uprising that threatens to overthrow 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.

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 Centre 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.

LAST, DESPERATE ACTS

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.

A Libyan man, Soula al-Balaazi, who said he was an opposition activist, told the network by telephone that Libyan air force warplanes had bombed some locations in Tripoli.

An analyst for London-based consultancy Control Risks said that indicated the end was approaching for Gaddafi.

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, said Julien Barnes-Dacey, Control Risks' Middle East analyst.

British Foreign Secretary William Hague said earlier that Gaddafi might be heading for Venezuela, which is ruled by his friend President Hugo Chavez, but a senior government source in Caracas denied that.

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.

Two Libyan fighter jets also landed unexpectedly in Malta on Monday, witnesses said. The office of Malta's prime minister said it was not clear whether the two pilots intended to ask for asylum. They initially had asked to refuel, it said.

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.

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 one of the eastern suburbs.

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 there were long queues for food and fuel as residents stocked up on essential goods, apparently anticipating new clashes after nightfall.

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

We will keep fighting until the last man standing, even to the last woman standing, he said on Sunday.

But people in Tripoli expressed anger at the speech.

A Libyan woman who gave her name as Salma, said: The speech was very, very bad.

The speech was very disappointing because he threatened the Libyan people with killing, hunger and burning. He did not offer mercy for the souls of the martyrs who were killed.

PROTESTERS CONTROL BENGHAZI

Gaddafi supporters were in central Tripoli's Green Square on Monday, waving flags and carrying his portrait.

Saif al-Islam's cajoling is unlikely to 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.

In the eastern city of Benghazi, protesters appeared to be largely in control after bloody clashes with troops and police.

Youths with weapons are in charge of the city. There are no security forces anywhere, University of Benghazi professor Hanaa Elgallal told Al Jazeera International television.

Salahuddin Abdullah, a self-described protest organiser, said: In Benghazi there is celebration and euphoria...The city is no longer under military control. It is completely under demonstrators' control.

There were reports that soldiers who refused to fire on civilians were executed by commanding officers in Benghazi.

We have buried today 11 bodies of soldiers who refused to fire on civilians and were executed by Gaddafi officers.. The bodies were cut, heads in one side and legs in the other...it is a crime what is happening here, said Elsanous Ali Eldorsi, a retired judge in Benghazi.

At least nine towns in the east, including Benghazi, Zuara and Zlitan, were under the control of protesters loyal to tribal groups, the president of the International Federation for Human Rights in France told Reuters.

Human Rights Watch said at least 233 people had been killed in five days of violence, but opposition groups put the figure much higher. Most were in Benghazi, a region where Gaddafi's grip has always been weaker than elsewhere.

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.