Forces loyal to Libyan leader Muammar Gaddafi have launched their first bombing raids on the main rebel-held city of Benghazi.
BBC correspondents in the city heard the sound of low-flying aircraft and explosions on the outskirts of the second city, which has a population of a million..
Reports say the targets included the city's airport at Benina.
A UN Security Council vote on action in Libya could be held later on Thursday.
Western countries want a no-fly zone to halt the advance of government forces.
The AFP news agency quotes a rebel spokesman as saying two of the planes attacking Benghazi were shot down.
Col Gaddafi's forces are reported to have seized positions from around rebel-held town of Ajdabiya, a key objective before launching a ground assault on Benghazi.
The Red Cross has announced that it is withdrawing from Benghazi because of the deteriorating security situation in the city.
'All necessary measures'
British Foreign Secretary William Hague said the latest draft United Nations resolution on Libya called for "all necessary measures short of an occupation force" to protect civilians under threat of attack.
"The resolution that is under discussion today includes demands for an immediate ceasefire, a complete end to violence, a ban on all flights in Libyan air space with the exception of humanitarian flights," he told MPs.
Following the toppling of the long-time leaders of neighbouring Tunisia and Egypt earlier this year, Libyan protesters started to demand that Col Gaddafi step down after 42 years of autocratic rule.
They quickly seized much of eastern Libya, but in recent days pro-Gaddafi forces have retaken several towns.
source : bbc.co.uk
