A defiant Muammar Gaddafi vowed on Saturday not to quit power in Libya but called for talks to end the conflict, even as his forces pressed their offensive against the key rebel-held port city of Misrata.

In an early-morning speech on Libyan television, the Libyan leader said Nato "must abandon all hope of the departure of Muammar Gaddafi.

"I have no official functions to give up: I will not leave my country and will fight to the death," he said, but also added a conciliatory note.

"We are ready to talk with France and the United States, but with no preconditions," Gaddafi said.

"We will not surrender, but I call on you to negotiate. If you want petrol, we will sign contracts with your companies — it is not worth going to war over.

"Between Libyans, we can solve our problems without being attacked, so pull back your fleets and your planes," he told Nato.

The veteran strongman insisted that the rebels battling his forces "are terrorists who are not from Libya, but from Algeria, Egypt, Tunisia and Afghanistan."

He also said that his people love him, that he is sacred and like a father to them — "more sacred than the emperor of Japan is to his people."

Witnesses reported two loud blasts at dawn on Saturday in Eastern Tripoli after Gaddafi's son, Seif al-Islam, vowed on Friday that Libya will "fight Nato for 40 years" if necessary.

"We will not raise the white flag of surrender," he said during a tour of hospitals to visit people wounded in Nato bombardments.

Meanwhile, the regime threatened to attack any ships trying to enter the lifeline rebel-held port of Misrata, after tanks launched an assault on the western city some 215 kilometres (130 miles) East of Tripoli.

Misrata's port is a crucial conduit for humanitarian aid to the city of half a million people, which Gaddafi's forces have been trying to capture for more than seven weeks.

Fierce fighting erupted around the city's airport on Saturday morning after several hours of relative calm overnight.

AFP journalists reported loud blasts and heavy machinegun fire from the direction of the airport after rebels said they destroyed at least four regime tanks advancing from the area.

A constant stream of casualties flowed into the main hospital in Misrata, where fighting has intensified 10 weeks after government forces launched a deadly crackdown on protests inspired by regime-changing movements in Tunisia and Egypt.

The Gaddafi regime said later it would attack "with force" any ship entering Misrata port.

State television also said the military had "put the port out of service," and that delivery of humanitarian aid to Misrata should now be carried out "overland and under the supervision of the armed forces."

Nato said three mines were found in the port early on Friday and were being disarmed.

"The mining of a civilian port by pro-Gaddafi forces is clearly designed to disrupt the lawful flow of humanitarian aid to the innocent civilian people of Libya," said Italian Navy vice-admiral Rinaldo Veri, calling it another "deliberate violation" of UN Security Council resolutions.

In Washington, the state department said secretary of state Hillary Clinton would attend a Libya Contact Group May 4-6 meeting in Rome to discuss how to help the rebels and protect civilians.

The group composed of Western countries, Turkey, Arab states, the United Nations, the Arab League and Nato, was set up in London on March 29.

Medics reported at least five people killed in Misrata on Friday and many more wounded.

"All of our operating theatres are full," Dr Khalid Abu Falra of the city's medical committee said. "Nato must quickly intervene, as in previous days."

The airport battle, just southwest of the city limits, followed barrages of rocket and mortar fire on the city.

Western Misrata also came under seemingly indiscriminate mortar and rocket fire on Friday, witnesses and medics said.

Forces loyal to Gaddafi, who has been in power for more than four decades, were pushed back from Misrata by the rebels and Nato air strikes on Monday, but remained within rocket range of the city.

The rebels said earlier in the week they had secured the port and that their next objective was the airport.

"Attack is the best form of defence," said Ibrahim Bet-Almal, who heads the rebel military forces in the area. "Gaddafi is sending reinforcements to the region every day."

British Brigadier Rob Weighill, director of Nato operations in Libya, said Nato warships stopped pro-Gaddafi forces on Friday from laying mines in Misrata harbour.

"Our ships intercepted the small boats that were laying them and we are disposing the mines that we found," Weighill told reporters via videoconference from his headquarters in Naples, Italy.

"It again shows his complete disregard for international law and his willingness to attack humanitarian delivery efforts," he said of Gaddafi.

In western Libya, Nato said its warplanes would focus on regime forces threatening the towns of Zintan and Yafran, scenes of heavy fighting between regime and rebel forces.

Fierce fighting which had raged for days for control of the Dehiba border crossing into Tunisia, meanwhile, hit a lull on Friday, but rebels expected a new offensive, witnesses said.

They said rebels retook the post late on Thursday in clashes that killed eight loyalist soldiers only hours after Gaddafi forces had overrun it.

A Tunisian police source said 5,150 people had crossed from Libya into Tunisia at Dehiba within 48 hours as the fighting raged.