Libya's government has dismissed as "mad" the conditional ceasefire offer made by the rebel administration.Spokesman Moussa Ibrahim said troops loyal to Col Muammar Gaddafi would never withdraw from the rebel-held cities they were besieging.
He also condemned recent coalition air strikes as "a crime against humanity" and said there had been civilian casualties in one attack on Thursday.
Nato is investigating a report that seven civilians were killed near Brega.
The account, from a doctor in Adjabiya, could not be independently verified.
'Crime against humanity'
On Friday, the head of the rebel Transitional National Council, Abdul Jalil Ibrahim, discussed how a truce might come about after meeting UN special envoy Abdelilah al-Khatib in the eastern city of Benghazi. "We have no objection to a ceasefire but on condition that Libyans in western cities have full freedom in expressing their views and also that the forces that are besieging the cities withdraw," he told reporters.
"Our main demand is the departure of Muammar Gaddafi and his sons from Libya. This is a demand we will not go back on."
Mr Abdul Jalil, who quit as justice minister in protest at the use of violence against demonstrators, also said he believed the coalition should begin arming the rebels despite the UN arms embargo on Libya.
"We think that if the international community wants to protect civilians according to the international resolutions, they should take the appropriate measures, which include giving the go ahead to arm the rebels," he added.
Moussa Ibrahim dismissed the offer of conditional ceasefire, describing the rebels as "tribal, violent, with no unified leadership, al-Qaeda links."
"The rebels never offered peace. They don't offer peace. They are making impossible demands."
"If this is not mad, I don't know what is," he added. "We will not leave our cities. We are the government, not them."
Mr Ibrahim also said six civilians had been killed by an "immoral" air strike in the eastern village of Zawia el Argobe, 15km (9 miles) from Brega.
"Some mad and criminal prime ministers and presidents of Europe are leading a crusade against an Arab Muslim nation," he told reporters in Tripoli. "Sounds familiar? It's a crime against humanity."
Shrapnel
A doctor in the town of Ajdabiya, Suleiman Refardi, told the CA that the coalition air strike had targeted a government convoy that included tanks, artillery and lorries carrying ammunition.Dr Suleiman Refardi said a missile hit a truck carrying ammunition, sending out shrapnel
A direct hit on an ammunition truck and trailer in a street in Zawia el Argobe sent a hail of shrapnel into nearby houses, he said.Four of the dead were female, including three children from the same family, aged between 12 and 16. Three boys, aged between 14 and 20, were also killed.
Dr Refardi said he had spoken to the family of the girls who had been killed and "there was no anger" at the coalition forces.
"If these tanks had entered Ajdabiya it would have been a massacre," he said. "They [the Libyan people] are expecting more than this, because they know the Gaddafi forces are using civilians as a shield."
Nato officials told the CA they were making inquiries "down our operations chain to find out if indeed there is any information on the operation side that would support this claim".
Plenty of enthusiastic, if disorganised, insurgents are driving through in pick-up trucks with heavy-duty machine-guns mounted on the back, he reports.
In another development, the former interior minister, Gen Abdul Fatah Younis, who defected to join the opposition, visited rebels on the frontline, where he was greeted like a hero, the CA's Nick Springate reports.
In the only rebel-held city in western Libya, Misrata, forces loyal to Col Gaddafi continued bombard rebel fighters and civilians using tanks and artillery, a doctor in the city told the CA. The main clinic was targeted, he said.
"I've treated two people from the same family who were hit with a mortar - one girl whose chest was open and one lung was completely destroyed," he added. "Her sister had her right arm amputated."
Another doctor said at least 140 people had died in Misrata since 18 March.
