TRIPOLI, Libya - Moammar Gadhafi stood defiant Tuesday in the face of the heaviest NATO airstrikes yet, at least 40 thunderous daylight attacks that sent plumes of smoke billowing above the Libyan leader's central Tripoli compound.

In late afternoon and as the strikes continued, Libyan state television broadcast an audio address from Gadhafi, 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 Gadhafi 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.

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Some 6,850 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 Defense Ministry.

It couldn't be confirmed whether Gadhafi's some 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!" Gadhafi 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-Gadhafi 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 Gadhafi believes NATO strikes are "not about civilians, democracy or peace in Libya. The attacks are about domination, revenge and wealth."

Gadhafi 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.