In an assault on Muammar Gaddafi's Mediterranean hometown, fighters loyal to the Libyan National Transitional Council are trying to fight their way into the city centre of Sirte from three fronts.
And fighters surged into into Bani Walid, another remaining Gaddafi bastion, in a campaign to break the back of regime holdouts.
NTC leaders described the offensive as a co-ordinated push to take Sirte - a city of about 100,000 people - from the south, east and west.
But their advance has been hindered by snipers among the loyalists of the toppled Libyan leader, as NATO warplanes flew overhead and smoke was seen rising from parts of the coastal city.
Meanwhile, Recep Tayyip Erdogan, the Turkish prime minister, is visiting Libya on Friday as part of his North African tour.
At least 11 NTC fighters have been killed and 34 wounded in the assualt on Sirte, according to a statement by the Misrata Military Council.
Al Jazeera's Hoda Abdel Hamid, reporting from Om Gandi, 90km from Sirte, said Gaddafi forces are reinforcing west of Harrawa towards Sirte.
"The latest information we have is that at the moment both sides are digging their heals around a town called Harrawa.
"One fighter who claims he came out of Sirte last night says revolutionary forces are controlling some areas inside Sirte. But the situation is quite dire for civilians there, he says. They are missing absolutely everything.
"He says they have been under siege by Gaddafi forces for at least three months."
A convoy of fighters had set out from Misrata, a port city, early on Thursday before splitting at the crossroads town of Abu Qurin, and a commander said they would approach Sirte in a pincer movement.
"We are turning the tables on Gaddafi. We were attacked in Misrata on three fronts, and now we're going to attack Sirte on three fronts," Fawzy Sawawy, commander of the Mountains Brigade, said.
Ali Gliwan, a member of the NTC's military council, said fighters who crossed a major highway overpass at the southwestern entrance of Sirte, were met by rocket fire from Gaddafi loyalists.
Jalal el-Gallal, a spokesman for Libya's new leaders, said several thousand fighters were involved, backed with tanks and mechanised vehicles.
The fighters advanced into the city centre, clashing with snipers holed up in a high-rise office tower - and with members of an elite unit of Gaddafi troops barricaded in a residence of the leader on the beach, Gliwan said.
He said four fighters on his side had been killed and seven wounded.
It was unclear how decisive the entry into Sirte was, however.
Last week, fighters claimed to have fought their way into another loyalist stronghold, Bani Walid, west of Sirte, but they were driven back by powerful resistance and their movement there has stalled.
Gaddafi's whereabouts remain a mystery, but his loyalists hold those two cities, the city of Sabha and other pockets in central and southern Libya.
The fresh assault came as the French and British leaders travelled to Libya on Thursday to congratulate the country's new rulers, the first visit by Western leaders since Gaddafi was ousted from power last month.
Gaddafi's spokesman, Moussa Ibrahim, criticised the joint visit to Tripoli by Nicolas Sarkozy and David Cameron, calling the aid provided by the two countries to the NTC a ploy "to get the oil and investments of Libya under the guise of reconstruction".