Rebels closed in on Moammar Gadhafi Friday, pushing back his fighters in a fierce battle in one key coastal city and seizing another town as they advanced toward his remaining bastion, the capital of Tripoli.

The territory remaining under Gadhafi's control has been shrinking dramatically in the past three weeks, with opposition fighters moving closer to Tripoli, a metropolis of two million people, from the west, south and east.

At the nearest point, rebel fighters are just 50 kilometres west of Tripoli, in the coastal city of Zawiya, where battles raged Friday over control of the city centre. Gadhafi's forces pounded rebel-held areas of the city with rockets, mortars and anti-aircraft fire, but by nightfall were pushed out of a multistorey hotel on the square.

NATO's bombing campaign has made it difficult for the regime to send massive reinforcements to Zawiya, enabling the rebels to maintain a hold over much of the city, their biggest prize in months.

But Friday's onslaught by regime forces also signaled that an opposition push toward Tripoli could be arduous and bloody. The massive fire at one point pinned down some two dozen rebel fighters behind a building about 200 metres from Zawiya's central square, a symbolic prize in the battle for control of the city of some 200,000 people.

The area was deserted, with building facades blackened and scarred by bullet holes.

The men took a break for Muslim noon prayers, washing their hands and feet with water from plastic bottles, then kneeling on carpets under an olive tree.

The group was commanded by Rida Shaeb, a 47-year-old electrician who wore his workman's blue coveralls to the front line. "We are here to fight," said Shaeb. "We are not going back, even if we die."

East of the capital, rebels seized the city of Zlitan after clashes with regime forces that left 31 rebels dead and 120 injured, a spokesman said. Zlitan had been a major obstacle in the rebels' push toward Tripoli from the east.

"The fighters have liberated Zlitan and they are fighting west of the city," said Munir Ramzi of the opposition Misrata Military Council. He said Gadhafi's forces were fleeing after Friday's victory and the rebels are in control of the city.

With the recent advances, the rebels cut off the coastal road to Tripoli from the east and the west, and also control a city along a major supply road to the capital from the south.

Early Saturday, a rebel spokesman said the strategic oil terminal of Brega in eastern Libya was completely under rebel control.

Ahmed Bani said that the industrial town of Brega was finally captured early Saturday morning.

Rebels have been fighting for control of Brega for over a week. Brega's capture is an important boost for the rebels because it contains Libya's second-largest hydrocarbon complex and is where the country's main oil fields feed into for refining.

Associate has allegedly defected

Dealing another blow to the increasingly isolated leader, Libyan rebels said Friday that Abdel-Salam Jalloud, a close Gadhafi associate who was once the No. 2 top regime official, has defected. Jalloud helped Gadhafi stage the 1969 coup that propelled him to power and transformed Libya from a monarchy to a republic. He was Gadhafi's most trusted deputy for two decades but began to clash with the leader starting in the 1990s.

Rebel spokesman Mahmoud Shammam said that Jalloud had fled to a rebel-held area in the western mountains and was on his way to Europe. Pictures showing Jalloud in the western town of Zintan appeared on rebel Facebook pages. Jalloud did not issue any statements, but Shammam said he had confirmed the defection on the telephone.

Jalloud's defection, if confirmed, would be the latest crack in what remains of Gadhafi's regime, although the two men had fallen out. Rebels also said Jalloud could provide valuable information about Gadhafi's inner circle.

Rebel official Abdel-Hafiz Ghoga said the defection "gives us assurance that Gadhafi is weakening" while stressing that Jalloud would face justice for any crimes committed when he was part of the regime.

Evacuations to begin in Tripoli

As fighting intensified, the International Organization for Migration announced plans to start evacuating "large numbers" of Egyptians and other foreigners, including some journalists, from Tripoli in coming days.

IOM spokeswoman Jemini Pandya said the organization has appealed to donors for emergency funding for the rescue effort, which was needed because the road between Tunisia and Tripoli has been closed.

"We have a very limited window of opportunity to carry out this operation because of the fighting, so it is essential that we are not constrained by a lack of funds from the outset," she told reporters in Geneva.

In recent weeks, the rebels gained momentum, following long stretches of deadlock in the six-month-old civil war. Fighting had erupted after anti-regime protests swept the country in February. In the early stages, the rebels seized much of the east and two pockets in the west, including the Nafusa mountain range and the port city of Misrata.

For the past week, rebel fighters have been bogged down in the centre of Zawiya, after claiming victory over a sprawling oil refinery complex on the western outskirts following days of fighting.

Rebel forces have frequently found themselves outgunned by Gadhafi's forces despite stepped up airstrikes by NATO in Zawiya, Tripoli and surrounding areas.

One gun shared by neighbours

Fisal Ben Issa, a 30-year-old lawyer-turned-fighter on Zawiya's front line, said he shares his Belgian-made assault rifle with a neighbour, each doing 12-hour shifts at the front line to get maximum use out of the weapon. Ben Issa was listing the weapons at Gadhafi's disposal when he was cut off by a particularly deafening round of mortar fire.

Shortly afterward, the group of two dozen fighters decided to disband, leaving the area in pickup trucks and on foot. Moments later, a tank captured by the rebels later started rumbling toward the centre of the city, firing several shells to the shouts of "God is great."

Just before nightfall, more than two dozen pickup trucks filled with rebel fighters and mounted with anti-aircraft guns charged forward into Zawiya. Witnesses and a rebel returning from the front line said the fighters had taken control of the central square and a hotel that had been a key regime sniper position, although government troops still held the main hospital.

The relentless shelling of Zawiya has sent many civilians fleeing. Others hunkered down in their homes, despite the risks.

Meanwhile, explosions shook Tripoli early Friday as NATO jets circled overhead. Flames lit up the Tripoli skies near Gadhafi's Bab al-Aziziya headquarters and army barracks.