A government spokesman said anti-Kadafi forces were advancing inside the city on several fronts but were meeting heavy resistance.

Meanwhile, forces loyal to the provisional government were streaming toward another pro-Kadafi bastion, Bani Walid, 95 miles southeast of Tripoli, the capital. Heavy fighting was reported inside the city, which has been under siege for a week.

Both battles are seen as critical by the provisional government that took control after rebels seized the capital last month, sending Kadafi and his allies fleeing after more than four decades in power. Kadafi and at least two of his sons remain fugitives.

On Thursday, British Prime Minister David Cameron and French President Nicolas Sarkozy paid a historic visit to the Libyan capital, praising the nation's revolution, urging Kadafi to surrender and sending a not-so-subtle message to Syria that room for autocratic rule was shrinking in the region.

Both nations played a leading role in the withering NATO air campaign that was essential in toppling Kadafi's rule. The two leaders were the first foreign heads of state to visit Libya since Kadafi was ousted from the capital last month and went on the run.

"This does go beyond Libya; this is a moment when the Arab spring can become an Arab summer," Cameron told a news conference with Sarkozy and leaders of Libya's transitional government.

Sarkozy used the opportunity to chastise the authoritarian government of President Bashar Assad in Syria, where security forces have used tanks and troops to combat a months-long protest movement.

"I hope that one day young Syrians can be given the opportunity that young Libyans are now being given," said Sarkozy, speaking with the other leaders at a Tripoli hotel.

The site of the media brief was subject to intense security. Attack helicopters flew overhead, roads were closed and armed troops of the transitional government stood guard along the main coastal road.

U.S. air power and intelligence-gathering capabilities were also key in the ongoing air operations over Libya, but the Obama administration has opted to let European nations take the lead role in the alliance campaign.

Both European leaders said Kadafi, who has urged his followers to fight a guerrilla war, should surrender.

"Let us be clear: This is not finished, this is not done, this is not over," Cameron said.

The NATO-led air mission over Libya will continue, they vowed, tying the aerial attacks to the fact that Kadafi remains at large and his loyalists still control or wield influence in large swaths of Libya.

"Kadafi has money, he has gold, he can buy mercenaries and he is still a threat, and therefore our mission is not finished," Sarkozy said.

The French president emphasized that there was "no hidden agenda" in the European air campaign, countering criticism that participating nations may be seeking oil deals and other contracts in the new Libya. "This was a just cause," Sarkozy said.

The head of Libya's transitional government, Mustafa Abdul Jalil, said that nations that assisted Libya in its struggle against Kadafi could expect "priority within a framework of transparency."

There has been speculation that some nations that were slow to endorse the anti-Kadafi uprising, notably China and, might lose out in future business deals with Libya.

Many nations, including France, Britain and the United States, along with Russia, China and Turkey, had business interests in Kadafi's Libya. The transitional government chief said that all contracts would be respected, if they had not been tainted by corruption.