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.
The UN Security Council adopted a resolution to ease economic and military sanctions against Libya and set up a UN mission to help the interim government, with officials in Tripoli saying a new lineup would be announced on Sunday.
Earlier, the General Assembly voted to give Libya's UN seat to the former rebel National Transitional Council.
Columns of NTC fighters backed by tanks launched an early morning assault on Sirte, Kadhafi's hometown on the central Mediterranean coast, a day after a first attack was repulsed.
Heavy fighting ensued at the airport and southeast of the city centre.
NTC forces fired anti-aircraft guns and heavy cannon within the city limits and Kadhafi fighters responded with sniper fire and Grad rockets.
Senior military commander Salem Jeah said NTC forces were nearing the centre of Sirte, with an AFP correspondent reporting late in the afternoon that the front line was about one kilometre away.
"We are advancing in from the west and the south towards the city centre," Jeah said. "Our forces retreated strategically during the night but are now speeding towards the centre and some have already entered."
Field commander Hadi Saleq 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.
The overall casualty figures were six dead and 35 wounded, based on an AFP hospital tally.
At least 200 NTC pick-up trucks had fanned out from a roundabout on September 1 Street firing heavy weapons to clear the area of Kadhafi fighters amid incoming sniper fire and sporadic rocket attacks.
Ironically, resident and university student Abdel al-Mutaly said it was not until Friday that he had learned Tripoli had fallen to the NTC on August 23.
There had been no electricity for a month, "so people were completely in the dark about what was going on outside" Sirte.
The NTC said its fighters had also entered the oasis town of Bani Walid southeast of Tripoli, but they made a "tactical withdrawal" in the evening due to sniper fire.
"It is useless to hold on to positions overnight in a hostile environment," a commander told AFP.
An NTC spokesman said earlier "our revolutionaries have entered Bani Walid," 170 kilometres (105 miles) southeast of the capital, adding with what proved to be excessive optimism that "the situation will be resolved this evening."
In New York, the Security Council lifted UN asset freezes and other measures against Libyan National Oil Corp and Zueitina Oil Co, and eased sanctions against the central bank, Libyan Arab Foreign Bank, Libyan Investment Authority and Libyan African Investment Portfolio.
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But measures against Kadhafi, his family and associates were maintained.
The council expressed concern at the "proliferation of arms in Libya and its potential impact on regional peace and security."
But the resolution allows arms supplies and technical assistance to the transitional government for the security of the authorities and for the protection of UN personnel, media and aid workers in the country.
A no-fly zone which has been used to justify NATO air strikes in Libya against Kadhafi targets was maintained, but Russian UN envoy Vitaly Churkin demanded that it be quickly reviewed, renewing allegations that NATO has diverted UN resolutions.
Earlier in the day, the UN General Assembly voted overwhelmingly to let the NTC take over Libya's UN mission.
That will allow NTC leader Mustafa Abdel Jalil to attend next week's UN gathering of world leaders in New York, where he is to meet US President Barack Obama and other key leaders on the sidelines of the meeting.
In Tripoli, meanwhile, an NTC official said a new government to be announced on Sunday would consist of 30 members and be representative of all political groups and regions, and that women would be included.
Turkish Prime Minister Recep Tayyip Erdogan was in Libya on Friday, boosting international support for the NTC a day after Britain's David Cameron and France's Nicolas Sarkozy became the first foreign leaders to visit the new Libya.
"I am happy to have been a witness to the advent of democracy in Libya," he said after joining Friday prayers.
He hailed "the memory of martyrs who sacrificed themselves for their country and their religion" and urged holdouts in Sirte and Bani Walid to "embrace your brothers and join other Libyans."
His visit came a day after Cameron and Sarkozy, whose forces spearheaded the NATO air war that helped topple Kadhafi, were mobbed by jubilant crowds in Tripoli and the eastern city of Benghazi.
But Kadhafi spokesman Mussa Ibrahim 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 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," he said, without disclosing where he was phoning from.
Sarkozy had insisted in Tripoli that there was "no ulterior motive" in Western assistance to the new Libya.
Ibrahim added "thousands" of loyalists were ready to fight "on all fronts" and that victory over the NTC forces was assured.
NATO has said about 15 percent of Kadhafi's forces were still operational.
Kadhafi and members of his inner circle have been in hiding since Tripoli was overrun, with the fugitive strongman still believed to be in Libya even though members of his family have fled to Algeria and Niger.
One of them, Kadhafi son Saadi, is being held in Niger, where the government said he would not be sent back "where he has no chance of receiving a fair trial and where he could face the death penalty."