In late afternoon and as the strikes continued, Libyan state television broadcast an audio address from Gaddafi, who denounced NATO and the rebels challenging his rule. He vowed never to surrender.
"We will not kneel!" he shouted.
Alliance officials warned for days that they were increasing the scope and intensity of their air campaign to oust Gaddafi after more than 40 years in power. NATO is backing the rebel insurgency, which has seized swaths of eastern Libya and pockets in the regime's stronghold in the west since it began in February, inspired by uprisings elsewhere in the Arab world.
Some 6850 people, nearly all of them Libyans, have streamed across the border from Libya to Tunisia since Monday to flee the NATO raids as well as fighting between the rebels and government forces, according to the Tunisian Defence Ministry.
It couldn't be confirmed whether Gaddafi's 10-minute speech was a live phone call or an audio recording, but it appeared to take state television by surprise. The sound was hastily adjusted to make it louder
"We will not surrender: we only have one choice - to the end! Death, victory, it does not matter, we are not surrendering!" Gaddafi said. Highlighting his anger, he called the rebels "bastards".
As he spoke, reporters in Tripoli heard the whooshing sound of low-flying military craft again, followed by several explosions. Pro-Gaddafi loyalists also fired celebratory gunfire in the air.
The Libyan leader also later appeared on state television sitting with tribal elders, said government spokesman Moussa Ibrahim. "He is still resilient," Ibrahim said, adding that Gaddafi believes NATO strikes are "not about civilians, democracy or peace in Libya. The attacks are about domination, revenge and wealth."
Gaddafi was last seen in a brief appearance on state television in late May. He has mostly been in hiding since NATO strikes in April targeted one of his homes. Libyan officials said one of his sons, Saif al-Arab, and three of his grandchildren were killed in that strike.
The sharp escalation in NATO strikes comes as the US and its allies step up efforts to break the virtual stalemate that has prevented both sides from achieving an outright victory.
"So what you're seeing across the country is an inexorable trend of the regime forces being pushed back, being incapacitated. You're seeing defections, oftentimes of some very high-profile members of the Gaddafi government, as well as the military. And I think it is just a matter of time before Gaddafi goes," President Barack Obama said during a joint news conference in Washington with visiting German Chancellor Angela Merkel.
Western reporters and a senior Libyan government official said the pounding airstrikes on Tuesday easily outstripped the number of bombing runs on any day since the international air campaign began in mid-March.
Ibrahim claimed some 31 people were killed in 60 NATO strikes on Tripoli. Previous government tolls have proven to be exaggerated.
Reporters, who face tight restrictions in the Libyan capital, saw only one dead man during a visit to Gaddafi's Bab al-Aziziya compound.
The dust-covered bloodied man was draped around a cement column at one of the crushed compound buildings. He was seen on a government-escorted tour of bombed sites.
The boot and legs of the man, identified as Misbah Hussein, in his 40s, stuck out from beneath a pile of twisted metal close to the remains of a building just inside the eastern entrance of the Gaddafi compound.
As his comrades realized what they were staring at, they rushed toward him, their arms raised.
"Bring a blanket!" one shouted.
They wrapped him in the closest thing they could find - a large green flag - green being the iconic colour of the Gaddafi regime.
A soldier said eight strikes targeted the building, which he said was a guest house for visiting dignitaries.
Around him, one building was smashed into three hulking cement parts and the floor was strewn with small chunks of metal, foam and cement.
He said some two dozen soldiers and civilians were sitting near the building when it was hit. He would not be named, citing military regulations.
A strike smashed another nearby building that officials identified as a guest house. The ground was littered with small grey shards.
That was not far from a zone where pro-Gaddafi supporters have camped in tents for the past few weeks to act as human shields against NATO strikes. Ibrahim, the regime spokesman, said the attacks would spawn "generations of revenge."
NATO issued no immediate comment on battering it delivered over Tripoli.
Gaddafi's inner circle has been shaken by a wave of defections. A Libyan rebel diplomat in Geneva said on Tuesday the country's labour minister Al-Amin Manfour - who had been representing Libya at the International Labor Organisation's annual meeting - has defected and joined the rebels.
Adel Shaltut said on Tuesday Manfour was on his way to the rebel stronghold of Benghazi, in eastern Libya. Shaltut and other diplomats at Libya's mission to the United Nations in Geneva defected to the rebels in February.
Russia, meanwhile, was renewing diplomatic efforts to end the civil war.
Mikhail Margelov, the Kremlin's special representative for Africa, said Gaddafi had lost his legitimacy but that NATO airstrikes were not a solution to the stalemate in Libya.
"As long as bloodshed continues the more difficult it will be to build a national reconciliation process after the civil war," Margelov told reporters on Tuesday during a visit to the eastern rebel stronghold of Benghazi.
Russia, along with China, abstained in the UN Security Council vote authorising the use of force against Libyan government loyalists and has repeatedly criticised the NATO bombing campaign in support of the rebels.
UN envoy Abdul-Elah al-Khatib also arrived in Tripoli, Ibrahim said, without providing details. And Libya dispatched Foreign Minister Abdul-Ati al-Obeidi to Beijing for a three days of talks, an apparent effort to restore some of Libyan government influence and defuse a setback delivered by China last week. Chinese officials announced on Friday that they had reached out to the rebel forces challenging Gaddafi, a significant effort to boost Chinese engagement in the Libya conflict and possibly jostle for a mediator role.
Chinese Foreign Ministry spokesman Hong Lei told reporters at a regular briefing on Tuesday that talks with al-Obeidi would focus on the need for a political solution to the Libyan crisis.
The revolt against Gaddafi followed popular uprisings that overturned the longtime rulers of Tunisia and Egypt. As the conflict escalated, it grew beyond an insurrection by a small group and has now evolved into a civil war.
