BENGHAZI, Libya – Libyan rebels on Monday rejected an African Union initiative for a ceasefire accepted by Moamer Kadhafi, and said the only acceptable solution was the ouster of the veteran strongman.

The rebel rejection came after NATO chiefs warned that any deal must be "credible and verifiable," and as alliance warplanes were again in operation against Kadhafi armour pounding the cities of Ajdabiya and Misrata.

US Secretary of State Hillary Clinton also stuck to US demands for Kadhafi to step down and leave Libya as part of a peaceful transition, but declined to comment on the proposed African Union deal until being fully briefed.

"We have made it very clear that we want to see a ceasefire, we want to see the Libyan regime forces pull back from the areas they have forcibly entered," Clinton told a news conference in Washington.

"We want to see humanitarian assistance reach the people of Libya. These terms are non-negotiable," she said.

"We believe, too, that there needs to be a transition that reflects the will of the Libyan people and the departure of Kadhafi from power and from Libya."

Rebel leader Mustafa Abdul Jalil told reporters in Benghazi that the African initiative has been surpassed.

"From the first day the demand of our people has been the ouster of Kadhafi and the fall of his regime," he said at a news conference in the rebel bastion.

"Kadhafi and his sons must leave immediately if they want to be safe... Any initiative that does not include the people's demand, the popular demand, essential demand, we cannot possibly recognise.

"We cannot negotiate with the blood of our martyrs. We will die with them or become victorious and with God's will we will be victorious," he said.

Abdul Jalil said the African initiative matched the UN Security Council calls for a ceasefire and the protection of civilians.

"This initiative that was presented today had been decided upon since March 10. A month has passed... during this long time Colonel Moamer Kadhafi did not respect these decisions, he bombed civilians with planes, missiles and rockets. He besieged cities with his forces. He placed security forces in civilian clothes inside city limits."

NATO said it struck more loyalist targets around Ajdabiya and Misrata on Sunday and Monday, destroying 11 Kadhafi regime tanks and five military vehicles.

And alliance chief Anders Fogh Rasmussen warned that warplanes will keep pounding Libyan forces as long as civilians are at risk.

"We appreciate all efforts to find a political solution to the problems in Libya, including the African Union initiative," Rasmussen said.

"But secondly I would also like to stress that the guiding principle for us will be how to implement the UN Security Council resolution fully, that is to protect the civilians against any attack."

Italian Foreign Minister Franco Frattini said Kadhafi and his sons should play no role in Libyan politics when a resolution is found to the current conflict.

He also said Abdul Jalil would visit Rome on Friday for talks with Italian leaders about Libya's future, after Italy became the third country along with France and Qatar to recognise the opposition as "sole interlocutor."

Shamsiddin Abdulmolah, a spokesman for the rebels' Transitional National Council, welcomed the African Union efforts, but demanded Kadhafi's overthrow.

"The people must be allowed to go into the streets to express their opinion and the soldiers must return to their barracks," he told AFP.

"If people are free to come out and demonstrate in Tripoli, then that's it. I imagine all of Libya will be liberated within moments."

He also demanded the release of hundreds of people missing since the outbreak of the popular uprising and believed to be held by Kadhafi's forces.

South African President Jacob Zuma said Tripoli had accepted the African Union plan for a ceasefire.

"We also in this communique are making a call on NATO to cease the bombings to allow and to give a ceasefire a chance," Zuma said.

But the rebels doubt the Libyan strongman would adhere to such a deal.

"The world has seen these offers of ceasefires before and within 15 minutes (Kadhafi) starts shooting again," Abdulmolah said.

The rebels have said they would negotiate a political transition to democracy with certain senior regime figures, but only on the condition that Kadhafi and his sons leave the country.

Near the eastern town of Ajdabiya, a doctor, Abdul Rahim Agouri, said that on Sunday they found one of the rebel helicopters shot down west of the town.

They recovered the bodies of three men from the scene and a fourth man, who was badly burned, was taken to hospital in Benghazi.

In Ajdabiya, an AFP correspondent saw more than a dozen burnt-out pick-up trucks which the pro-Kadhafi fighters had fitted with heavy machine guns for their abortive offensive on the front line between the rebel-held east and the mainly government-held west.

Many of the bodies that the rebel fighters buried close to the battlefield on the town's western outskirts were charred beyond recognition after a NATO strike, combined with their own efforts to repulse the loyalist assault.

"We found 35 bodies in total, maybe two or three more melted into the vehicles," said Muftah Jadallah, 63, as the last of the burials took place.