Libyan diplomats at the United Nations have called for international intervention to stop their government's violent action against demonstrators.
The most senior Libyan diplomat in Washington said he cannot represent his country any more.
Libya's leader, Colonel Gadaffi, has made his first appearance on national television since the crisis erupted and dismissed reports that he had fled amid the unrest sweeping the country.
Speaking to state TV from outside a ruined building, he said "I am in Tripoli and not in Venezuela," after rumours that he had flown to Caracas.
Colonel Gaddafi's statement came after security forces and protesters clashed in the capital for a second night. Witnesses said warplanes and helicopters had fired on protesters and Arabiya television said at least 160 people had died.
The United Nations Security Council is to meet in closed session to discuss Libya.
UN Secretary-General Ban Ki-moon made the announcement, after speaking to Colonel Gaddafi on Monday. Mr Ban said he had urged the colonel to protect human rights and freedom of assembly and of speech.
The BBC's correspondent monitoring events in Libya from Cairo says Colonel Gaddafi has now lost the support of almost every section of society.
Libya's deputy ambassador to the United Nations, Ibrahim Dabbashi, has called on Colonel Gaddafi to step down, and accused his government of genocide. Mr Dabbashi says these are the leader's "end days" and he should be put on trial.
Airport packed with people fleeing
Tripoli's airport is packed with passengers of different nationalities trying to leave the country, the BBC reports.
In the city, the streets are almost empty except for armed police or security with civilian outfits, who are on every corner.
Mobile phone networks are down and even landlines can't be used for international calls. Burnt-out buildings are smouldering in several locations, and as the sun sets, there is heavy gunfire in the city centre and planes flying overhead.
Largest tribe backs protesters
The eastern cities of Benghazi and al-Bayda now appear to be largely under the control of protesters, and two tribes, including the country's largest, have backed them.
Three other senior diplomats besides Mr Dabbashi have defected to the protesters' side, and the Justice Minister has also quit, objecting to the "excessive use of violence" against demonstrators.
The most senior diplomat in Washington, Ali Adjali, says he is supporting the protesters in Libya. He says he has worked in the Libyan foreign service for 40 years but cannot support his government any more.
Two military fighter pilots have defected to Malta, after being ordered to bomb protesters.
Some international firms, including oil giant BP, are preparing to pull their staff out of Libya.
The US-based monitoring group Human Rights Watch says more than 230 people have been killed in Libya since the unrest began last week.