The United States has accused Muammar Gaddafi of defying international demands for an immediate ceasefire, and France's UN envoy predicted military action within hours of an international meeting on Libya on Saturday.
Libya's government announced on Friday an immediate ceasefire against pro-democracy protesters, hours after the United Nations Security Council authorised a no-fly zone over the country.
The unilateral ceasefire declaration, however, appeared to have done little to convince outside powers to hold off on plans for air strikes to force an end to an increasingly bloody civil war.
Residents in the rebel-held city of Misurata said they faced heavy bombardment through the night on Friday -- a charge the government denied -- while a US official said Gaddafi's forces were still advancing towards the rebels' eastern stronghold Benghazi.
Within hours of Barack Obama, the US president, saying the terms of a UN resolution meant to end fighting in Libya were non-negotiable, his UN envoy, Susan Rice, asked by CNN whether Gaddafi was in violation of these terms said; "Yes, he is".
''Military intervention within hours''
France, which along with Britain has been leading a drive for military intervention, will host a meeting on Saturday on Libya which will be attended by US Secretary of State Hillary Clinton and Arab leaders.
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"Tomorrow we will have a summit in Paris with all the major participants in the operations and in the diplomatic effort. So I think it would be a good moment to send the last signal," the French ambassador to the United Nations told BBC's Newsnight.
"So I guess that after this summit, I think that in the coming hours, I think we will go to launch the military intervention," Ambassador Gerard Araud said.
Obama made clear any military action would aim to change conditions across Libya -- rather than just in the rebel-held east -- by calling on Gaddafi''s forces to pull back from the western cities of Az Zawiyah and Misurata as well as from the east.
"All attacks against civilians must stop," Obama said on Saturday, a day after the UN Security Council passed a resolution authorising international military intervention.
"Gaddafi must stop his troops from advancing on Benghazi, pull them back from Ajdabiya, Misurata and Az Zawiyah, and establish water, electricity and gas supplies to all areas. Humanitarian assistance must be allowed to reach the people of Libya ...
"Let me be clear, these terms are not negotiable... If Gaddafi does not comply ... the resolution will be enforced through military action."
Reports of clashes
Libya's eastern rebel stronghold of Benghazi was braced for the worst on Friday night after rumours that Gaddafi's troops were within striking distance of the Mediterranean city.
Hundreds of men, some riding in pick-up trucks mounted with machine guns, flooded out of the city in response to a call from Benghazi's rebel-run radio to swiftly man their posts.
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Several loud explosions, some of them followed by anti-aircraft fire, were heard inside Benghazi and new checkpoints sprang up as word spread that Libyan leader Gaddafi's forces could be on their way.
There was no immediate confirmation that government forces had moved closer to the city and his deputy foreign minister, at a news conference in Tripoli, denied there were any plans to attack the rebel bastion.
"The armed forces are now located outside the city of Benghazi and we have no intention of entering Benghazi," Khaled Kaim told reporters.
Kaim acknowledged that checkpoints had been set up outside rebel-held cities, but stressed that "any sovereign country is free to take [security] measures".
In Misurata, which like Az Zawiyah has been left stranded in the west while rebels who had advanced towards them from the east were beaten back by a counter-offensive by Gaddafi forces, residents said they had faced heavy bombardment on Friday.
One doctor said at least 38 people had been killed in the assault launched on Friday morning.
Another doctor, who declined to give his name, said by telephone late on Friday evening, "now they are on the outskirts of the city. I can still hear bombing from time to time".
In Tripoli the government said there had been no bombing since it announced the ceasefire.
"We have had no bombardment of any kind since the ceasefire was declared," Khaled Kaim, Libya's deputy foreign minister, said when asked about reports of continued government operations in Misurata and other parts of the country.