Libyan rebels made a renewed effort to push towards the oil port of Brega while Muammar Gaddafi's forces pounded besieged Misrata to the west with rockets and mortars, a rebel spokesman said.

Underlining the difficulties faced by the rebels, six were killed and 16 wounded when Gaddafi loyalists fired rockets at a group of insurgents driving along the exposed coastal' highway from the town of Ajdabiyah west towards Brega.

The rebels' attempt to fight their way into western Libya - which would eventually allow them to link up with comrades in Misrata - has ground to a halt along the eastern coastal stretch from Ajdabiyah to Brega, despite Nato air strikes.

Rebels said some fighters had set up positions on the outskirts of Brega, but with their forces exposed to attacks on the highway - and often fleeing back in response - they were unable to send more men forward to dislodge Gaddafi loyalists in the town centre.

In Misrata, besieged for seven weeks, a rebel spokesman, Gemal Salem, said Gaddafi's forces pounded the town with rockets and mortars on Saturday, targeting a diary factory and another that makes cooking oil.

He said three people were killed and more than 20 wounded.

The US-based Human Rights Watch has accused Gaddafi's forces of using cluster bombs -- which scatter bomblets over a wide area - in Misrata. The Libyan government has rejected the allegations.

In Ajdabiyah, rebels said Gaddafi's forces were ensconced in the centre of Brega, often inside houses while insurgent fighters were themselves more exposed.

'We have people on the edge of Brega, we control that area only. Nothing has changed inside Brega,' said Mohammed el-Misrati, 20, after returning to Ajdabiyah to the east.

Gaddafi's forces have been bombing the road from Ajdabiyah to Brega for several days, sometimes firing from a distance, sometimes approaching in cars.

'We were in our vehicles and they opened fire with rockets,' Abdulrazek, one of the men hit by Saturday's attack, said, while groaning in pain in the emergency room of Adjabiyah hospital.

Outside the facility, medics collected blood-soaked bandages and scrubbed stretchers clean of blood.

Sustained anti-aircraft fire was heard coming from the north and northeastern sections of Tripoli, Gaddafi's power base, on Saturday evening, a Reuters correspondent in the capital said. What sounded like distant explosions could also be heard, but it was not known what had caused them.

Stalemate

On Friday, US President Barack Obama acknowledged the military situation on the ground in Libya had reached a stalemate, but said he expected Nato allies to force Gaddafi from power eventually.

Obama, British Prime Minister David Cameron and French President Nicolas Sarkozy published a joint newspaper article vowing to continue their military campaign until Gaddafi leaves power.

They acknowledged their aim of regime change went beyond protecting civilians, as allowed by a U.N. Security Council resolution, but said Libyans would never be safe under Gaddafi.

'Our duty and our mandate under UN Security Council Resolution 1973 is to protect civilians, and we are doing that. It is not to remove Gaddafi by force. But it is impossible to imagine a future for Libya with Gaddafi in power,' they wrote.

The United States led the bombing campaign in its first week, but has since taken a back seat, putting Nato in command on March 31 with the British and French responsible for most of the air strikes.

US Secretary of State Hillary Clinton said the Nato allies were searching for ways to provide funds to the insurgents, including helping them to sell oil from areas they control.

'The opposition needs a lot of assistance, on the organisational side, on the humanitarian side, and on the military side,' she said.

Rebel leader Younes told Al-Arabiya on Friday the insurgents had secured weapons from friendly nations, but gave no details.

With the rebels bogged down in the east, aid groups and residents have described an increasingly desperate situation for many trapped civilians in Misrata, with few areas safe from the fighting and a lack of food and medical supplies.

Hundreds of civilians are believed to have been killed, although details are impossible to verify independently.

'The (government) forces are still firing mortars at residential areas. There are clashes in Tripoli Street. Three people were killed today,' Salem, the rebel spokesman, said.

Tripoli Street is a main thoroughfare in the city of roughly 300,000, Libya's third largest, and has been the frequent scene of fierce fighting in recent weeks.

Another rebel spokesman said government forces fired at least 100 Grad rockets into the city early on Saturday, targeting an industrial area close to the port where thousands of migrants are stranded and awaiting evacuation.

'The (Gaddafi) forces have focused their shelling on that area in the past few days because they want to scare away ships bringing aid or aiming to evacuate migrants,' Abdelbasset Abu Mzereiq said by telephone.

A resident who arrived in Tunisia on Saturday said the fighting in Misrata was getting worse by the day.

Ibrahim Ali, 22, came on board a Medecins Sans Frontieres aid ship, accompanying a neighbour who was seriously wounded in a shelling attack. Sixty-four other wounded people from Misrata were also taken to safety on board the ship.

'They are bombing residential areas day and night. It's non-stop and they are using bigger weapons,' he said in a hospital in the town of Sfax. 'They bomb roads, houses.'

Food was running short in some areas but people were trying to help each other out, and electricity was on and off. 'Many shops are closed. At the bakeries there are long queues.'

Some streets where heavy fighting was taking place were fast becoming unrecognisable. 'The destruction is total ... .'

Asked who was controlling most of the city, Ali said: 'It's 50-50. It can change quickly.'

A Red Cross team arrived in the city on Saturday to assess the situation there, the Geneva-based International Committee of the Red Cross and a Libyan government spokesman said.

Libyan officials say they are fighting armed militia with ties to Al Qaeda bent on destroying the large North African oil-exporting country, and they deny that government troops are bombarding Misrata.-Reuters