Sustained gunfire erupted in the centre of Libya's capital, Tripoli, an area that has so far been relatively free of violence.
It was unclear who was carrying out the shooting, which started early on Sunday, or what caused it, Anita McNaught, Al Jazeera's correspondent in the capital, said.
Automatic weapon rounds, some of it heavy calibre, echoed around central Tripoli along with pro-government chants, whistling and a cacophony of car horns as vehicles sped through the vicinity, witnesses said.
However, a government spokesman denied any fighting was under way in Tripoli. "I assure you, I assure you, I assure you, I assure you, there is no fighting going on in Tripoli," Mussa Ibrahim told the Reuters news agency.
"Everything is safe. Tripoli is 100 per cent under control. What you are hearing is celebratory fireworks. People are in the streets, dancing in the square."
Our correspondent, reporting from Green Square in Tripoli, said that thousands of people had turned out to show their support to Libyan leader Muammar Gaddafi.
“The square is absolutely thronged with supporters of Gaddafi,” McNaught said. But she added that some of these 'supporters' had admitted to a fellow British journalist on Sunday that they were in fact army and police personnel in civillian clothes.
Tripoli is the main stronghold of Gaddafi, who is facing a sustained rebellion that has posed the biggest challenge ever to his more than 41-year-old rule.
Libyan state television said the shots in Tripoli were in celebration of Gaddafi forces having reclaimed the cities of Misurata and Az-Zawiyah, which lies just 50km west of the capital, a day after anti-government fighters repelled repeated attacks by forces loyal to Gaddafi.
The Libyan government has announced widespread tax cuts to mark what it called "victory" over the rebels.
Gaddafi's forces on Sunday continued to launch counter-attacks on anti-government rebels along the central Libyan coast, with airstrikes and ground battles reported in Bin Jawad, Ras Lanuf and Misurata.
However, residents of Misurata told Al Jazeera that reports the city had been recaptured were false.
"There's absolutely no grounds for that claim whatsoever," Sadoun Mistrai, one resident, said.
However, since then residents said government tanks had begun shelling the town.
"Misurata is currently under attack," a resident told Al Jazeera.
Reporting from Ras Lanuf, Al Jazeera's Jacky Rowland said an aircraft flew in and dropped a bomb on the area on Sunday.
"We think that the pilot was targeting some heavy anti-aircraft guns that were along the roadside," Rowland reported.
The area, in the country's central coast, houses a major refinery and petrochemical complex.
Ras Lanuf, and the nearby town of Bin Jawad, have seen fierce fighting between Libyan government forces and rebels, with reports of opposition fighters having shot down a government helicopter earlier on Sunday.
After Sunday's air attack caused some rebels to briefly flee the area, Rowland reported rebels again heading west toward the front-line.
"We are seeing people loading up with ammunition and guns, vehicles and also ambulances, tearing down the road, pressing forward in the direction of Bin Jawad, which is a town about 30-40km to the west of here, where there is still fighting going on in the streets between pro and anti Gaddafi forces," she said.
Earlier on Sunday, rebels said they had come under sniper fire and air attack on the frontline.
"They claim that there were some very young people up on rooftops shooting down at them and they said that they were then attacked from the air,” Rowland said.
While the rebels have a strong presence in Ras Lanuf, they told our correspondent the town was still held by Gaddafi loyalists.
"What we're seeing is a lot of movement, for the first time in days," Rowland said, adding that the rebel forces are completely disorganised, constantly swinging between euphoria and panic.
"I think that their biggest strength, as far as the rebels are concerned, is the sheers numbers of volunteer fighters. People with no previous military experience came to the call, learning pretty quickly how to operate ... an anti-aircraft carrier."
Hoda Abdel-Hamid, Al Jazeera's correspondent, had earlier said that anti-Gaddafi forces told her they are gaining ground in the area surrounding the capital and may be as close as 40km to Sirte, a Gaddafi stronghold.
"The rebels have advanced easily through many other towns, where they have been met with general support, the battle for Sirte is likely to be much tougher," she said.
"Some people fear the big battle will be there."
The Associated Press news agency reported that Libyan warplanes had launched air strikes on an anti-Gaddafi force advancing towards the city of Sirte
An AP television crew saw the air strikes targeting the anti-Gaddafi forces on Sunday, the news agency reported.
State TV meanwhile showed pictures of tanks, armoured-personnel carriers and other weapons it said were seized on Saturday from rebels in Az-Zawiyah.
But witnesses told Al Jazeera rebel forces there were able to repel heavy government assaults on their positions on Saturday when Gaddafi's forces encircled the city.
More than 30 people were killed and as many as 200 people were said to have been wounded in the fighting that drove government forces out of the town.
Youssef Shagan, a spokesman for the fighters in the town, said that Gaddafi's forces had entered Az-Zawiyah at 6am (04:00 GMT) with hundreds of soldiers, along with tanks and armoured vehicles.
Gaddafi's forces had broken through defences into Martyrs' Square, in the heart of the town, but hours later were pushed back, Shagan said.
Benghazi, Libya's second city, is the stronghold of protesters and is firmly in the hands of anti-government forces, but Libyan state television said on Sunday that forces loyal to Gaddafi are on their way to take back the city.
Source: Al Jazeera and agencies