Gaddafi troops assault rebel-held Libyan town Ajdabiya
Libyan rebels have denied claims that pro-Gaddafi forces have taken Ajdabiya - the last town before their headquarters in Benghazi.
The BBC's Jon Leyne in Benghazi says that, after heavy bombardment, government soldiers have made their first ground assault on the town.
The advance by troops loyal to Libya's leader comes ahead of the UN Security Council discussing a no-fly zone.
The UK, France and Lebanon have called for this in a draft resolution.
Rebel leaders want the international community to prevent pro-Gaddafi forces from using aircraft against them.
However, countries such as the US, Russia, China and Germany are understood to harbour doubts about imposing a no-fly zone. Some are wary of foreign military intervention in the conflict.
The Arab League has backed the idea but Tuesday's meeting of G8 foreign ministers in Paris failed to do so.
Pro-Gaddafi forces are also reported to again be shelling Misrata - the only western city in rebel hands.
"Very heavy bombardments are taking place now from three sides. They are using heavy weapons including tanks and artillery. They have yet to enter the town," a resident called Mohammed, told the Reuters news agency by telephone.
Massacre feared
Col Muammar Gaddafi's allies say they are now in control of Ajdabiya but rebel leaders say the assault was repelled.
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Ajdabiya is 160km (100 miles) from Benghazi, Libya's second city, and also controls the road to the Egyptian border.
Our correspondent says the situation in Benghazi is getting more tense by the hour and the calls for a no-fly zone more desperate.
Jalal al-Gallal of the National Libyan Transitional Council said that there would be a "massacre" if the international community did not intervene.
"He [Gaddafi] will kill civilians, he will kill dreams, he will destroy us," he told the BBC.
Col Gaddafi's son Saif al-Islam told Euronews TV that: "Everything will be over in 48 hours" even if a no-fly zone is imposed.
But our correspondent says that government announcements that an attack on Benghazi is about to begin appear to be propaganda designed to unnerve the opposition.
Even if Ajdabiya falls, the government does not seem to have enough troops in the field to attack the city of one million people, he says.
However, medical aid agency Medecins Sans Frontieres (MSF) on Wednesday announced that it was pulling its staff out of Benghazi due to the heavy fighting.
It said it would continue to send supplies to health facilities in Libya.
Gaddafi speech upside-down
French Foreign Minister Alain Juppe on Wednesday used his blog to condemn the slow response of the international community to the situation in Libya.
"Only the threat of force can stop Gaddafi. It is by bombarding, with the few dozen planes and helicopters he really has, his opponents' positions that the Libyan dictator has turned the balance," he wrote.
We can/could neutralise his airborne means by targeted strikes."
He also said that several - unnamed - Arab nations were prepared to take part in such action.
Italy's Foreign Minister Franco Frattini, however, ruled out military intervention, according to Reuters.
"We cannot have war, the international community should not, does not want and cannot do it," he told a hearing of a parliamentary commission in the Senate.
Italy, which ruled Libya for three decades, has close relations with Col Gaddafi.
On Tuesday, there was fierce fighting around Brega. The oil town has changed hands several times over recent days and reports have suggested the rebels have lost control.
Meanwhile, in a TV speech, Col Gaddafi taunted the UK and France.
"Britain no longer exists. It is a trace of what it used to be. It has been promoting attack on Libya. Is there a common border between us? Are you our guardian? By what right?" he said.
He went on to "dare" the US, Britain and France to "give their people freedom like I did to the Libyan people".
Our correspondent says the defiant speech was projected upside-down onto a big screen in the main square of Benghazi.
He says people threw shoes at the screen in a traditional expression of their contempt for Col Gaddafi.