Muammar Gaddafi's forces are waging counterattacks on anti-government rebels along the central Libyan coast, with air raids and ground battles reported in Bin Jawad, Ras Lanuf, Az-Zawiyah and Misurata.
Gaddafi is facing an uprising since February 17 that poses the biggest challenge ever to his four-decade rule over the oil-rich north African nation.
Bin Jawad was reclaimed by government forces on Sunday, but opposition rebels continued to advance on the area amid conflicting claims about the capture and recapture of several strategic Libyan cities and towns.
Sources report deadly clashes took place in the area, that lies in the middle of the coastline between the opposition stronghold of Benghazi and the capital, Tripoli, over which Gaddafi retains a tight grip.
Injured opposition fighters had been taken to the local hospital in nearby Ras Lanuf, a rebel-held town.
Rebels in Misurata also beat back Gaddafi's forces in heavy fighting that left 18 people killed, a local doctor told the Reuters news agency.
Gaddafi meanwhile made a fleeting appearance on Libyan state television on Sunday night, but disappeared almost immediately.
Crowds were seen celebrating and shouting the leader's name as he appeared in Tripoli's Green Square, but no explanation was given as to why state TV did not stay with footage of the president. They instead cut back to the studio, going on to a separate interview.
This comes after heavy shooting was heard in Tripoli early on Sunday. The government said there was no violence in the capital, and called the shots "celebratory fireworks".
Mussa Ibrahim, the Libyan government spokesman 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."
It was unclear who was carrying out the shooting, or what caused it, Al Jazeera's Anita McNaught reported from the city.
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.
"I assure you, I assure you, I assure you, I assure you, there is no fighting going on in Tripoli," Ibrahim said.
Our correspondent, reporting from Green Square, said that thousands of people had turned out to show their support for Gaddafi.
“The square is absolutely packed with supporters of Gaddafi," she said, adding that some of these "supporters" had admitted to a British journalist on Sunday that they were army and police personnel in civilian clothes.
Libyan state television said the shots in Tripoli were in celebration of the government forces' success in reclaiming the cities of Misurata, about 200km east of Tripoli, and Az-Zawiyah, just 50km west of the city, a day after anti-government fighters repelled repeated attacks by forces loyal to Gaddafi.
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.
Our correspondent said "locals [in the Green Square] are still out on the street celebrating a military victory that hasn't happened ... you have to wonder what these people have been told".
Later, residents of Misurata said government tanks had begun shelling the town.
"Misurata is currently under attack," a resident told Al Jazeera.
Reporting from north-central Libya, somewhere between Bin Jawad and Ras Lanuf, Al Jazeera's Tony Birtley said there had been four air attacks in the area on Sunday, one of which was witnessed by Al Jazeera's Jacky Rowland.
Reporting from Ras Lanuf, 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," she said.
The area, in the country's central coast, houses a major refinery and petrochemical complex.
Both Ras Lanuf and Bin Jawad have seen fierce fighting between Libyan government forces and rebels, with opposition fighters reported to have shot down a government helicopter on Sunday.
After an air attack caused some rebels briefly to flee the area, Rowland reported that the men were again heading west towards the frontline.
"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 to 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. Al Jazeera's Birtley said rebels were coming under "quite a sizeable force" of heavy resistance from pro-Gaddafi forces.
He described the rebel groups as being "driven by enthusiasm and not really experience".
While the rebels have a strong presence in Ras Lanuf, they told Al Jazeera's Rowland that the town was still held by Gaddafi loyalists.
"What we're seeing is a lot of movement, for the first time in days," she said, adding that the rebel forces are completely disorganised, constantly swinging between euphoria and panic.
Al Jazeera's Anita McNaught reports from Libya's capital Tripoli on 'victory celebrations' by Gaddafi supporters
"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."
Earlier on Sunday, the Associated Press news agency reported that Libyan fighter jets had launched attacks on an anti-Gaddafi force advancing towards the city of Sirte.
In another development, Libyan state TV 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 that rebel forces there were able to repel heavy government assaults on their positions when Gaddafi's forces encircled the city.
More than 30 people were killed and as many as 200 people are feared to have been wounded in the fighting that drove out government forces.
Youssef Shagan, a spokesman for the fighters in Az-Zawiyah, said that Gaddafi's forces had entered the city at 6am local time (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 city, 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 were on their way to take back the city.
Against this backdrop of continued fighting, the UN Security Council will name Portugal to head its Libya sanctions committee, Al Jazeera has learnt.
Guido Westerwelle, the German foreign minister, became the latest political figure on Sunday to call for fresh sanctions against Gaddafi.
Meanwhile, the European Union has sent experts into Libya to get "real time" information on humanitarian and evacuation efforts there.
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"I have decided to dispatch this high level mission to provide me with first-hand, real-time information to feed into the discussions leading up to Friday's extraordinary European Council when I will update heads of state and government on the situation," Catherine Ashton, EU foreign minister, said on Sunday.
On the other side of the Atlantic, John Kerry, the chairman of the US Senate Foreign Relations Committee, said once again that the US and its allies should plan for a no-fly zone over Libya.
His remarks come just days after Robert Gates, the US defence secretary, said that a no-fly zone was tantamount to going to war because it would call for attacking Libya's air defences.
In Sunday's other developments, it was reported that three Bangladeshi nationals were found dead and 11 went missing after they jumped from an evacuation vessel off the coast of Greece.
This was in a bid to prevent being sent back to Bangladesh.
Firas Kayal, of the United Nation's refugee agency, UNHCR, told Al Jazeera between 12,000 and 15, 000 people - most of them from Bangladesh - have crossed the border from Libya into Tunisia over the last couple of days.
There are plans to try and arrange a chartered flight to transport them home, he said. Kayal said that a total of around 100, 000 people have already crossed the border between Libya and Tunisia.
Thousands are fleeing the unrest in Libya, many being flown out of neighbouring Tunisia. Four US military aircraft carrying more than 300 Egyptian refugees left for Cairo on Sunday, but many nationals from other countries are still stranded with nowhere to go.