NATO has launched a fourth night of airstrikes on Tripoli, leaving smoke rising from Libyan leader Muammar Gaddafi's compound where five loud blasts were heard in the vicinity.
Several large explosions rocked the capital late on Thursday night and a column of smoke was seen rising from Gaddafi's Bab al-Aziziyah base.
The latest attacks come only hours after Libya's government proposed a ceasefire to end more than three months of fighting and the start of unconditional talks with the opposition.
Spain said it was one of several foreign states contacted by Al-Baghdadi Ali Al-Mahmoudi, the Libyan prime minister, with an offer of an immediate ceasefire based on an existing African Union roadmap to resolve the conflict, which, crucially, does not mention Gaddafi's future.
The rebels insist they want any government initiative to include the Libyan leader's departure as a first step.
"We welcome any initiative which starts with the departure of Gaddafi, his sons and his regime from Libya," Mustafa Abdel Jalil, the head of the rebel Transitional National Council, told Al Jazeera.
But White House deputy national security adviser Ben Rhodes, speaking in Deauville, said the United States did not see the new Libyan ceasefire offer as credible.
Libya was not complying with UN demands and its forces were still attacking population centres, so the United States would continue with the military campaign, he told reporters.
UK to deploy helicopters
Britain’s government has now also given clearance for the use of its attack Apache helicopters in ousting Gaddafi.
If NATO decides to use attack helicopters, it would mark a shift in the coalition's strategy which has so far relied on fighter planes.
David Cameron, the British prime minister, who joined Western leaders at the Group of Eight summit in the French seaside resort of Deauville, avoided discussing the matter which has caused tension between Britain and France. France has already said it would deploy attack helicopters.
Nicolas Sarkozy, the French president, the most vocal Western leader on Libya, told reporters on Thursday that Gaddafi still had the option of remaining in his country but he should step down and call off his forces.
"We are not saying that Gaddafi needs to be exiled, that's not our problem," he said in Deauville.
"When we say he must leave, he must leave power and the quicker he does it, the greater his choice."
Sarkozy added that Gaddafi must send his troops back to their barracks in exchange for any ceasefire agreement, and that a rebellion against his government was making "real progress".
Attempts to build a consensus at the summit on Libya may be prevented by Russia, which opposes the NATO bombing.
Russia has been tasked by the G8 to help defuse the stalemate. Gaddafi denies that his troops target civilians and say his security forces were forced to act to put down a rebellion by criminals and members of al-Qaeda.
On Thursday, forces loyal to Gaddafi launched the heaviest bombardment on the rebel-held city of Misurata for days.
Rebel spokesmen in Misurata, scene of some of the fiercest fighting in Libya's three-month conflict, said a mortar attack there had killed three rebels.
Suleim Al-Faqih said the Misurata clashes started when rebels attacked Gaddafi forces who were using an excavator to dig a trench to block a road: "We fired on them and advanced. They fell back and started firing mortars."
At a news conference in Misurata, Fathi al Bashaagha, a member of the town's military council, said rebel forces advanced 4km west on Thursday and destroyed weapons depots belonging to Gaddafi loyalists before falling back to their frontline on Misurata's outskirts.
The military council said it had no immediate plans to advance on Zlitan, the next major town west on the road to Tripoli, which is currently held by Gaddafi loyalists.