Libyan government forces attacked the coastal city of Misrata with at least 100 Grad rockets early on Saturday, a rebel spokesman said.

"They fired Grads at an industrial area this morning, at least one hundred rockets were fired. No casualties are reported," Abdelbasset Abu Mzereiq told Reuters by telephone. "We know that the dairy factory there has been damaged."

Human Rights Watch said it had evidence that Gaddafi's forces were firing cluster munitions into residential areas of Misrata.

It published photographs of what it said were Spanish-produced cluster bombs, which release grenades designed to explode into fragments and kill the maximum number of people.

Mussa Ibrahim, a Libyan government spokesman, dismissed the allegations: "I challenge them to prove it."

By pledging not to end the air war until Gaddafi leaves power, the US, French and British leaders have raised the stakes. They have ruled out sending ground troops, but it remains to be seen whether air power alone will be enough to dislodge a leader who has held power firmly for 41 years.

A rebel spokesman in Misrata said pro-Gaddafi forces had shelled both the centre and the road leading to the port, a lifeline for trapped civilians and the main entry point for international aid agencies, killing eight people on Friday.

Doctors in the besieged Libyan city of Misrata have released patients early to deal with new wounded from fighting because of capacity problems, a Medecins Sans Frontieres (MSF) doctor said on Friday.

"They are overwhelmed with casualties," MSF Dr Morten Rostrup told Reuters by satellite phone. "They got 30 new wounded yesterday and in order to take care of them they had to discharge some patients earlier than they wanted to ... to have capacity to treat the new wounded."

Rostrup spoke from on board an aid ship operated by the charity that departed Misrata on Friday for Tunisia carrying some 65 wounded -- some in critical condition -- from fighting between rebels and pro-Gaddafi forces.

The ship docked in the port of Libya's third largest city on Friday morning after failing to do so on Thursday due to heavy bombardment. Rostrup said he had visited Misrata hospitals to assess which patients he could bring back to Tunisia.

"They (medics) are dealing pretty well. They have some equipment ... They lack a neurosurgeon, which is a problem," Rostrup said.

Rebels defending Misrata, their last major enclave in western Libya and the scene of heavy fighting in recent weeks, say the situation is getting worse each day.

They said a government rocket attack on a residential district killed 23 civilians on Thursday and that heavy shelling forced closure of its port, a lifeline for the besieged western city.

Residents say they and thousands of stranded migrant workers face shortages of basic foodstuffs and medical supplies and have only sporadic water and electricity.

Rostrup said a MSF team had visited a camp inhabited primarily by sub-Saharan Africans desperate to leave. "They want to leave the city ... (they) live in very miserable conditions," he said.

"They are living around a road, there is some water provided to them but they complain about not having much food. They don't have proper shelter. They use plastic sheeting and blankets."

He said patients travelling back to Tunisia mainly suffered from gunshot or shrapnel wounds. Around 10 were critically ill.

"We are continuously stabilising patients, we give them fluids, antibiotics," he said. "I'm happy that my patients so far are stable, I just really hope they will continue to be so."