Deep cracks opened up in Colonel Muammar Gaddafi's regime after more than 40 years in power, with diplomats abroad and the justice minister at home resigning, air force pilots defecting and a fire raging at the main government hall after clashes in the capital Tripoli.

At sunset, pro-Gaddafi militia drove around Tripoli with loudspeakers and told people not to leave their homes, witnesses said, as security forces sought to keep the unrest that swept eastern parts of the country — leaving the second-largest city of Benghazi in protesters' control — from overwhelming the capital of 2 million people.

State TV said the military had "stormed the hideouts of saboteurs" and urged the public to back security forces. Protesters called for a demonstration in Tripoli's central Green Square and in front of Gadhafi's residence, but witnesses in various neighborhoods described a scene of intimidation: helicopters hovering above the main seaside boulevard and pro-Gaddafi gunmen firing from moving cars and even shooting at the facades of homes to terrify the population.

Youths trying to gather in the streets were forced to scatter and run for cover by the gunfire, and at least one young man was shot to death late Monday night, said one witness, who like many reached in Tripoli by The Associated Press spoke on condition of anonymity for fear of reprisal.

Gaddafi, whose whereabouts were not known, appeared to have lost the support of at least one major tribe, several military units and his own diplomats, including the delegation to the United Nations. Deputy U.N. Ambassador Ibrahim Dabbashi accused Gaddafi of committing genocide against his own people in the current crisis.

Warplanes swooped low over Tripoli in the evening and snipers took up position on roofs, apparently to stop people outside the capital from joining protests, according to Mohammed Abdul-Malek, a London-based opposition activist in touch with residents.

Communications to the capital appeared to have been cut, and residents could not be reached by phone from outside the country. State TV showed video of hundreds of Gaddafi supporters rallying in Green Square, waving palm fronds and pictures of the Libyan leader.

State TV quoted Gaddafi's son, Seif al-Islam, as saying the military conducted airstrikes on remote areas, away from residential neighborhoods, on munitions warehouses, denying reports that warplanes attacked Tripoli and Benghazi.

The first major protests to hit an OPEC country — and major supplier to Europe — have sent oil prices jumping, and the industry has begun eyeing reserves touched only after Hurricane Katrina in 2005 and the first Gulf War in 1991.

Tripoli was largely shut down today, with schools, government offices and most stores closed, except for a few bakeries, said residents, who hunkered down in their homes. Armed members of pro-government organizations called "Revolutionary Committees" hunted for protesters in Tripoli's old city, said one protester named Fathi.

Members of the militia occupied the city center and no one was able to walk in the street, said one resident who lived near Green Square described a "very, very violent" situation.

"We know that the regime is reaching its end and Libyans are not retreating," the resident said. "People have a strange determination after all that happened."

Another witness said armed men dressed in militia uniforms roamed the capital's upscale diplomatic neighborhood and opened fire on a group of protesters gathering to organize a march. People wept over the dead.

Residents hoped that help would arrive from the other parts of the country.