Reporting from Cairo — Moammar Kadafi's embattled regime unleashed a military assault in the heart of the Libyan capital in an effort to crush a popular protest like those that have already toppled two North African rulers and now threatens the longest-serving leader in the Arab world.
Unlike the strongmen who fell to street demonstrations in Tunisia and Egypt, Kadafi all but launched a war against his country's civilian population to maintain control of the oil-rich nation.
Libyan state television reported Monday that security forces were storming what it called "dens of terror and sabotage" in the capital, Tripoli. Security forces firing live rounds and tear gas regained control of the city's main square from demonstrators who had massed there, according to witnesses and media reports.
Independent Libyan news websites reported that 150 to 200 people were killed in the daylong violence.
But fast-moving developments suggested that after 41 years, Kadafi's regime could be crumbling from within.
Divisions appeared in the army, and police in several cities switched sides. Several powerful tribal leaders also defected. One tribe threatened to stop pumping oil, the lifeblood of the economy, if violence against protesters continued.
Nearly the entire Libyan delegation to the United Nations, as well as other senior diplomats, condemned the military crackdown and called for international intervention to stop the violence.
Diplomat Adam Tarbah said the U.N. delegation, with the exception of the ambassador, decided to distance itself from Kadafi's government "because of the regime's despicable actions to attack the Libyan people."
"We are aware that this will put our families back home in danger, but they are in danger anyway," said Tarbah, a nine-year veteran of the diplomatic service.
Two Mirage fighter jets from Libya landed on the Mediterranean island nation of Malta, and the pilots asked for political asylum. There were conflicting reports that they had fled because protesters had seized their air force base near Tripoli, or because they had refused orders to fire rockets at the protesters who now control Benghazi, Libya's second-largest city. Neither report could be confirmed.
Kadafi, 68, made a brief appearance on state television early Tuesday to deny that he had fled the country. "I'm still here," he said. It was not clear whether he was at his command compound at the Bab al Aziziya military base on the edge of Tripoli or whether he had gone to his hometown of Sirt, his desert base of Sabha or elsewhere.
In Washington, Secretary of State Hillary Rodham Clinton urged Libya "to stop this unacceptable bloodshed." But officials acknowledged that they had minimal influence over Kadafi.
"If the issue is survival of the regime, the Libyan leaders are not going to care what the international community thinks or what it does," said a senior Obama administration official. "It's a deteriorating situation, and you can't discount the possibility of a civil war."
The State Department ordered nonessential U.S. Embassy personnel and family members to leave Libya and advised Americans to delay travel to the country. U.S. Ambassador Gene Cretz left Tripoli in December amid concerns for his safety because of WikiLeaks cables in which he described Kadafi as exhibiting increasingly erratic behavior, a U.S. official said. With Libyan tribes apparently choosing sides, fighting could rage for some time, U.S. officials said.
Libya is closed to foreign reporters, and authorities restricted telephone and cellphone access. But amateur videos, telephone interviews and Twitter messages portrayed a nation in the throes of a ferocious upheaval, by far the most lethal since a string of uprisings erupted across North Africa and the Middle East six weeks ago.
Protests have flared from Morocco to Iran, and have dislodged the autocratic rulers of Tunisia and Egypt.
The clashes in Libya appeared to escalate hours after Seif Islam Kadafi, the president's son, appeared on television early Monday.
Wagging his finger repeatedly, he warned that security forces had been told to restore order "at any price" to prevent civil war. Streets would "run with blood," he declared, if demonstrators didn't return to their homes.
Battles were reported in Tripoli's downtown as rampaging protesters stormed the state broadcasting building. Libya's Al Jamahiriya 2 television and Al Shababia radio were both forced off the air temporarily, but they resumed broadcasting later in the day.
Firefighters battled blazes inside the Interior Ministry and parliament, where the extent of the damage was unclear. Amateur videos showed crowds cheering outside a burning police station.