Forces of the new Libyan regime were forced to retreat Saturday after earlier pushing deeper into Sirte, a hometown of ousted leader Muammar Gaddafi, in the deadliest of three days of fierce clashes.

Rocket, sniper and heavy artillery fire left at least 24 National Transitional Council (NTC) fighters dead and more than 40 wounded, including a French freelance videographer.

"The situation at the roundabout is pitiful. There is no central command, we are retreating to regroup and re-enter again from three fronts," said Al-Dhahira Brigade commander Saleb Abu Shaala.

Pro-Gaddafi forces in Sirte, the ousted leader's hometown, have put up stubborn resistance against thousands of former rebel fighters massed in and around the key town.

Abu Shaala said the clashes erupted at about 10:30 am (0830 GMT) Saturday and that Gaddafi's forces used heavy artillery and rockets against them while the anti-Gaddafi forces hit back with Grad Rockets.

Abdel Nasser al-Sheikh, of the Misrata Military Council, charged that the pro-Gaddafi troops were firing from the Bin Hamal mosque.

"We cannot attack this place," he said.

"There is progress but snipers remain a problem," said fighter Fatha Allah, 18, returning from a frontline he said had moved closer to the coast.

"We reached up to the city centre but there are families there."

Six hours after the fighting began, NATO warplanes flew overhead, while the roar of artillery fire faded after rebels broke past a key roundabout in the city's south, which was the scene of heavy fighting on Friday.

But convoys of NTC fighters left Sirte again under rocket fire late Saturday, failing to secure their advances in what has proved a recurring pattern in seven months of conflict.

Front-line fighters and commanders gave contrasting reports of their progress in Sirte, with men on the ground acknowledging they were facing a tough and well-trained enemy while those in charge downplayed the pockets of pro-Gaddafi resistance.

"We don't even have five percent of Sirte because we just go in and out," said Abdul Rauf al-Mansuri, one of those taking up arms for the new authorities.

He said that, despite the massive deployment of armed vehicles in and around the town, only a minority of the men were doing the heaviest of the fighting.

Mansuri added that NTC forces did not control large swathes of the city as claimed by a top commander in Misrata and that they had also lost their advantage by pulling back at night, giving Gaddafi's men time to re-arm.

"If we controlled the city, we would sleep there, but we don't," he said.

On the outskirts of Sirte, a medic with half his face blown away was among the first men killed and brought in from the front lines.

Khaled Safati "was a gentleman and very kind man who always said he wasn't afraid to die," said Dr Ali Maitiga, fighting back tears.

"He went to the front to bring back the injured but came back dead," he added. The nearest major hospital is 460 kilometres away in Libya's third city of Misrata.

Other medics wept as Safati's body was brought in, and repeatedly shouted "Allahu akbar" ("God is greatest") before taking on an endless flood of casualties, an AFP reporter witnessed.

French freelance video journalist Olivier Sarbil was among the seriously wounded after he was struck by shrapnel' He was evacuated to Misrata by helicopter for further medical attention.

Commander Salem Jeha said there were at least 1,200 NTC armed vehicles and some 6,000 fighters, mostly from Misrata, deployed in the Sirte area to take on the die-hard Gaddafi loyalists.

"There may be houses and pockets of resistance, but they will not be able to overcome the rebels' massive forces," he said, adding that he had received reports that half of the city's civilians had fled.

The attacking fighters were trying to prevent civilian casualties in the city of some 130,000 people and were not seeking revenge: "We are not using heavy weapons except to protect our rebels when they are targeted."

A pick-up truck arrived at a checkpoint 30 kilometres west of Sirte bearing three prisoners whom the NTC forces said were Gaddafi snipers, an AFP correspondent reported.

One, an old man, showed signs of having been beaten, with blood streaming from his temple.

The youngest prisoner managed to blurt out that he was 19 as an angry crowd of fighters ringed the vehicle and tried to beat the trio. Others held them back, however, shouting that there were media present.

"Sahafa, sahafa (journalists, journalists)" they yelled.