Forces loyal to Libya's Muammar Gaddafi have launched a fierce counter-attack in the fugitive leader's stronghold of Bani Walid while putting up resistance in his hometown of Sirte.
Despite the heavy fighting, Ahmed Bani, the interim government's military spokesman, said on Saturday that it was only a "matter of days" before the two towns are captured.
He also gave army personnel still loyal to Gaddafi a last chance to join the ranks of former rebel fighters.
"The soldiers and officers who will not heed this last call will be accused of high treason," Bani said in Tripoli. Their integration was part of efforts to rebuild the national army in a post-Gaddafi Libya, he said.
Al Jazeera's Anita McNaught, reporting from Wishtata about 50km from the centre of Bani Walid, said there had been no fighting planned for Saturday on that front.
"But forces loyal to Gaddafi attacked from within and took potshots at the [NTC fighters] ... Their artillery aim is pretty good these days," our correspondent said, after receiving reports of numerous casualties.
"Today was for consolidation and lessons learned from yesterday, which ultimately achieved little more than getting people killed and demonstrating the strength of pro-Gaddafi forces."
In Bani Walid, medical and NTC sources said six NTC fighters were killed on Friday and 20 wounded.
The NTC said its fighters had entered the oasis town, 180km southeast of the capital Tripoli, but they made a "tactical withdrawal" on Friday evening due to sniper fire.
"It is useless to hold on to positions overnight in a hostile environment," a commander said.
In Sirte, NTC forces swept further into the city before retreating under heavy artillery fire after two hours of clashes.
At least 6,000 fighters battled in and around one of Gaddafi's final strongholds.
"The situation at the roundabout is pitiful," Saleb Abu Shaala, the Al-Dhahira brigade commander, said. "There is no central command, we are retreating to regroup and re-enter again from three fronts."
Abu Shaala said the clashes erupted in mid-morning and that Gaddafi's forces used heavy artillery and rockets against them.
Doctors at a field hospital reported at least 10 killed and 40 wounded in the fighting in Sirte.
Front-line fighters and commanders gave contrasting reports of progress in Sirte, with men on the ground acknowledging they were facing a tough enemy and those in charge downplaying the pockets of resistance.
Al Jazeera's Hoda Abdel Hamid, reporting from Ras Lanuf near Sirte, said it had been very difficult for some NTC fighters to get inside the town.
"In the east, they have not been able to even get close to town. The fighters here have heavy weaponry - tanks, heavy artillery - but they are still not able to advance," she said.
"We don't even have five per cent of Sirte because we just go in and out," Abdul Rauf al-Mansuri, an NTC fighter, said.
Deaths in NATO air raids
Moussa Ibrahim, Gaddafi's spokesman, claimed NATO had carried out extensive air strikes on Sirte, killing 354 people overnight. He said Gaddafi was personally leading "all aspects of the struggle".
In a call to the Reuters news agency on Saturday, Ibrahim said: "NATO attacked the city of Sirte last night with more than 30 rockets directed at the city's main hotel and the Tamin building, which consists of more than 90 residential flats.
"In the last 17 days, more than 2,000 residents of the city of Sirte were killed in NATO air strikes."
The claims could not be verified independently, as Sirte has been largely cut off from communication since the fall of Tripoli last month.
"We are aware of these allegations," Colonel Roland Lavoie, spokesman for the Western military alliance, said in Brussels."It is not the first time such allegations have been made. Most often, they are revealed to be unfounded or inconclusive."
Fighters backing the NTC on Saturday seized Hirawa, a small town 60km from Sirte.
They danced in the streets singing "Gaddafi, we will burn you" and ripped down posters of the fugitive former strongman, stamping on his face in the dirt.
The anti-Gaddafi fighters, who had hurtled into Hirawa on scores of machine gun-mounted pickup trucks and tanks, said they had taken power with very little difficulty.
"We advanced into Hirawa after about five days of heavy fighting and NATO bombing," fighter Nouri al-Fanoussi said. "We managed to save the town very smoothly this morning without any resistance."
The armed forces of the new Libyan leadership are also consolidating their control over southern desert towns near the pro-Gaddafi stronghold of Sabha, the main southern urban centre about 650km south of Tripoli.
Upon reaching Mahruqa about 100km from Sabha on Friday, former rebel forces encountered resistance from pro-Gaddafi holdouts after being invited into the town by elders.