Fierce battle raged between the rebels and Gaddafi forces, which bombarded the western besieged town of Misurata as a rights watchdog accused the Libyan regime of targeting civilians by using cluster bombs.

For the third day in a row, troops loyal to Gaddafi shelled Misurata with at least 100 Grad rockets. Libyan troops, which has besieged the coastal town for over six weeks, pounded Misurata on Friday as well, killing at least eight people. Al Jazeera quoted local doctor as saying that seven other civilians, including children and older people, were wounded in that attack. Residents around 120 rockets pounded Misurata, the lone rebel bastion in western Libya, 214 kilometres east of Tripoli.

Renewed fighting erupted near the key eastern town of Ajdabiya, where rebels, bolstered by NATO air strikes, are regrouping on the road to the oil town of Brega, 80-km west of Ajdabiya, BBC said. NATO warplanes have intensified their air strikes targeting Libyan troops even as the 28-member NATO alliance squabbled over stepping up the military operations.

With the pro-government troops showing desperation to take over Misurata, Human Rights Watch (HRW) accused the Libyan regime of firing cluster bombs into residential areas.

"Human Rights Watch observed at least three cluster munitions explode over the El-Shawahda neighbourhood in Misurata on the night of April 14, 2011," the New York-based group said in a statement.

The rights watchdog said its researchers have inspected the submunition and interviewed ambulance drivers who saw two other strikes that appeared to have been carried out with cluster bombs.

"This is urban warfare of the nastiest kind. On the one hand you have the rebels fighting the government and on the other government forces appear to be randomly shelling and using sniper fire in civilian areas," BBC reported. However, the government has dismissed the charge. "I challenge them to prove it," Mussa Ibrahim, a Libyan government spokesman, was quoted as saying by the pan-Arab channel.

Cluster bombs, which cause indiscriminate deaths in civilian populations when used, are forbidden under international law.

Amid fears of a stalemate in the conflict, leaders of US, UK and France have vowed to intensify the military campaign in Libya to force Gaddafi to quit as NATO bombed the capital Tripoli on Friday. Even as differences came out among world powers over the air strikes in Libya, US President Barack Obama, French President Nicolas Sarkozy and British Prime Minister David Cameron made it clear that there can be no peace in the country till Gaddafi stepped down.

BBC quoted Abdullah, a doctor in Misurata, as saying that he had seen evidence of the use of cluster bombs, which are banned by more than 100 countries.

It was 'appalling' that Libya was using such weapons, especially in a residential area, said Steve Goose, HRW's arms division director. "They pose a huge risk to civilians, both during attacks because of their indiscriminate nature and afterward because of the still-dangerous unexploded duds scattered about," he underlined.

Pro-Gaddafi forces are also using the Soviet-designed Grad rocket system to shell Misurata, which is faced with sever food shortages and electricity and communications lines have been cut. Amid deep division among world leaders on the military operation in Libya, a key meeting of NATO foreign ministers in Berlin saw several members rebuffing calls from France and Britain for additional combat aircraft for air strikes.

The western alliance is struggling to overcome differences over the Libya mission, with Britain and France seeking more strikes by other NATO nations, particularly the U.S. Only few of NATO's 28 members are taking part in the air strikes, with key nations such as Spain and Italy reluctant to be involved in the bombings on Gaddafi's forces.

The US, which was spearheading the air campaign in Libya till March 31, has taken a back seat and has allowed British and French warplanes to take the lead.

On the diplomatic front, top leaders from BRICS group -- Brazil, Russia, India, China and South Africa -- said "the use of force should be avoided."

In the Chinese city of Sanya on Thursday, they collectively voiced their opposition to the use of force in Libya and pitched for a central role for the United Nations and regional organisations in resolving the matter. However, Obama, Sarkozy and Cameron have underlined that leaving Gaddafi in power would be an 'unconscionable betrayal' of the Libyan people.

"It is unthinkable that someone who has tried to massacre his own people can play a part in their future government," the leaders said in a jointly written article published in the International Herald Tribune on Thursday. "So long as Gaddafi is in power, NATO and its coalition partners must maintain their operations so that civilians remain protected and the pressure on the regime builds," they said.

Meanwhile, rights groups have warned that the situation in Misurata is critical amid fears of a humanitarian disaster.

The International Organisation for Migration (IOM) said on Friday that a ship with nearly 1,200 Asian and African migrants left Misurata for Benghazi, the 'capital' of the opposition transitional council.