Heavy gunfire broke out in Tripoli today as forces loyal to Muammar Gaddafi tightened their grip on the capital.
But anti-government protesters claimed control of many cities elsewhere and top government officials and diplomats turned against the long-time leader.
While cities in the eastern half of the country celebrated, raising the flags of the old monarchy, the mood in Tripoli was bleak. Residents were afraid to leave their houses, saying pro-Gaddafi forces were opening fire randomly in the streets.
International outrage mounted a day after Gaddafi vowed to defend his rule and called on supporters to crack down on anti-government protesters.
Gaddafi's retaliation has already been the harshest in the Arab world to the wave of anti-government protests sweeping the Middle East.
Italy's Foreign Minister Franco Frattini said estimates of some 1,000 people killed in the violence in Libya were "credible," although he stressed information about casualties was incomplete. Human Rights Watch has put the death toll at nearly 300, according to a partial count.
The fighting in Tripoli came as the opposition reportedly seized control of Misrata, with witnesses saying people were honking their horns and raising pre-Gaddafi flags from the monarchy to celebrate.
Misrata would be the first major city in the west to fall to anti-government forces, which have mainly been concentrated in the east.
Faraj al-Misrati, a local doctor, said six residents had been killed and 200 injured since February 18, when protesters attacked offices and buildings linked to Gaddafi's regime.
He said residents had formed committees to protect the city, clean the streets and treat the injured.
"The solidarity among the people here is amazing, even the disabled are helping out," he said.
New videos posted by Libya's opposition on Facebook and youtube also showed scores of anti-government protesters raising the flag from the pre-Gaddafi monarchy on a building in Zawiya, on the outskirts of Tripoli. Another showed protesters lining up cement blocks and setting tires ablaze to fortify positions on a square inside the capital.
Gaddafi defiantly vowed to fight to his "last drop of blood" and urged his supporters to strike back against Libyan protesters to defend his embattled regime in a televised speech yesterday that served as an all-out call for his backers to impose control over the capital and take back other cities.
After a week of upheaval, protesters backed by defecting army units have claimed control over almost the entire eastern half of Libya's 1,000-mile Mediterranean coast, including several oil-producing areas.
Celebratory gunfire by Gaddafi supporters rang out in Tripoli after the leader's speech, while in protester-held Benghazi, Libya's second-largest city, people threw shoes at a screen showing his address, venting their contempt.
One woman who lives near central Tripoli said heavy gunfire erupted today as armed Gaddafi backers and mercenaries hired from other countries opened fire.
She said the streets were empty and even injured people couldn't go to the hospital for fear of being shot.
Gaddafi appears to have lost the support of at least one major tribe, several military units and his own diplomats, including Libya's ambassador in Washington, Ali Adjali, and deputy UN Ambassador Ibrahim Dabbashi.
The Libyan Embassy in Austria also condemned the use of "excessive violence against peaceful demonstrators" and said it was representing the Libyan people.
International alarm has risen over the crisis, which sent oil prices soaring to the highest level in more than two years yesterday and sparked a rush by European and other countries to get their citizens out.
The UN Security Council held an emergency meeting that ended with a statement condemning the crackdown, expressing "grave concern" and calling for an "immediate end to the violence" and steps to address the legitimate demands of the Libyan people.
French President Nicolas Sarkozy also pressed for European Union sanctions against Libya's regime because of its violent crackdown on protesters