Fighters loyal to Libya's new leaders on Friday thrust deep into the city of Sirte and into desert oasis Bani Walid, two of fugitive Moamer Kadhafi's few remaining bastions, AFP reporters said.
On the political front, Turkish Prime Minister Recep Tayyip Erdogan was in Tripoli, boosting international support for the National Transitional Council (NTC) a day after Britain's David Cameron and France's Nicolas Sarkozy became the first foreign leaders to visit the new Libya.
Columns of NTC fighters backed by tanks launched the assault late morning on Sirte, Kadhafi's hometown 360 kilometres (225 miles) west of Tripoli, after a first attack on Thursday was repulsed by loyalists, who set up sniper nests on rooftops.
An AFP reporter witnessed heavy fighting at the airport and two kilometres (about a mile) southeast of the city centre, with NTC forces firing anti-aircraft guns and heavy cannon within the city limits and Kadhafi forces responding with sniper fire and Grad rockets.
Senior military commander Salem Jear, also a member of Misrata Military Council, told AFP that NTC forces were nearing the centre of Sirte.
"We are advancing in from the west and the south towards the city centre," he said by telephone. "Our forces retreated strategically during the night but are now speeding towards the centre and some have already entered."
Field commander Hadi Saleq of the Karama (Generosity) Brigade, who has 160 men under his command and who himself has roots in Sirte, reported skirmishes on three fronts.
"The fighting is concentrated on September 1 Street, residential zone 2 in the city centre and around the airport," Saleq said.
There was no immediate indication of casualties, but the NTC said it had lost 11 fighters on Thursday, with 34 wounded. It added that 40 Kadhafi loyalists had been captured.
An NTC spokesman in Tripoli, meanwhile, said the new regime's fighters had also entered the oasis town of Bani Walid southeast of Tripoli, where an AFP photographer witnessed fighting at the market.
"Our revolutionaries have entered Bani Walid," Mahmud Shammam said of the town 170 kilometres (105 miles) from the capital without elaborating, adding only that "the situation will be resolved this evening."
Turkish premier Erdogan flew from Tunisia to Tripoli airport, where he was greeted by NTC chief Mustafa Abdel Jalil.
"I am happy to have been a witness to the advent of democracy in Libya," he said after joining Friday prayers in the capital's Martyrs Square -- formerly Green Square under Kadhafi's regime.
Erdogan hailed "the memory of martyrs who sacrificed themselves for their country and their religion, as did Omar Mukhtar," the resistance fighter against Italian colonists who was hanged 80 years ago by the Italian military.
"I address myself to Sirte and Bani Walid: embrace your brothers and join other Libyans," Erdogan said, as the fighting in the two strongholds raged.
"Unification in the ranks will help Libyan development and make it one of the best countries in the region," he added.
The Turkish premier began his tour in Egypt, where he received a rapturous welcome, confirming his rising regional status.
His visit comes a day after Cameron and Sarkozy, whose forces spearheaded the NATO air war that helped topple Kadhafi, were mobbed in Tripoli and the eastern city of Benghazi.
The two leaders are immensely popular among ordinary Libyans for their role in ending the fugitive strongman's 42 years of iron-fisted rule.
Kadhafi's spokesman Mussa Ibrahim, however, accused them of coming to plunder Libya's riches.
"The visit marks the start of a project of colonisation of Libya," Ibrahim charged in a telephone call late on Thursday to Syria-based Arrai television.
"They are hurrying to collect the fruits of the fall of Tripoli... because they obviously fear the arrival of America and other countries wanting a slice of the cake," he said, without disclosing where he was phoning from.
Kadhafi and members of his inner circle have been in hiding since Tripoli was overrun late last month, with the fugitive strongman still believed to be in Libya even though members of his family have fled to Algeria and Niger.
"They hurried to Tripoli to make secret deals with the collaborators and the traitors, and to take the control of oil and investments under the pretext of rebuilding," Ibrahim said.
He added that "thousands" of loyalists were ready to fight "on all fronts" and that victory over the NTC forces was assured.
The NTC's advance towards Sirte appeared to have been made easier by NATO air strikes.
NATO said that on Thursday its warplanes had struck one military storage facility, two armed vehicles, one tank, four multiple rocket launchers and eight missile systems.
Around 15 percent of Kadhafi's forces are still operational, the alliance has said.
In Tripoli, Cameron at a joint news conference with Sarkozy on Thursday pledged help to bring the Kadhafi to book.
"We must keep on with the NATO mission until civilians are all protected and until this work is finished," he said.
"We will help you to find Kadhafi and to bring him to justice."
Sarkozy insisted there was "no ulterior motive" in Western assistance to the new Libya.
"We did what we did because we thought it was right," he declared.