TRIPOLI/UNITED NATIONS (Reuters) - The United Nations authorised military attacks on Muammar Gaddafi's forces, but his forces closed in on the Libyan rebels and he vowed to storm their stronghold with "no mercy, no pity".
French diplomatic sources said action could follow within hours, and could include France, Britain and possibly the United States and one or more Arab states. A U.S. military official said no immediate U.S. action was expected.
Gaddafi's son Saif al-Islam said on Friday that Libya was "not afraid" of the U.N. move, Al Arabiya television reported.
Time was running short for Benghazi, the eastern city that has been at the heart of Libya's month-old revolt.
But Gaddafi's troops did not fulfil his threat to overrun the rebel base overnight after their rapid counter-offensive brought them to within 100 km (60 miles) of the eastern city.
"We will come. House by house, room by room," Gaddafi said in a radio address to Benghazi late on Thursday.
Al Jazeera television showed thousands of people listening to the speech in a central Benghazi square, then erupting in celebration after the U.N. vote, waving anti-Gaddafi tricolours and chanting defiance of the man who has ruled for four decades.
Fireworks burst over the city and gunfire rang out.
The U.N. Security Council, meeting in emergency session, passed a resolution endorsing a no-fly zone. It also authorised "all necessary measures" -- code for military action -- to protect civilians from Gaddafi's forces.
While other countries or NATO may play roles in military action, U.S. officials expect the United States with its extensive air and sea forces to do the heavy lifting in a campaign likely to include air strikes on tanks and artillery.
Gaddafi warned Benghazi residents that only those who laid down their arms before his advancing troops would be spared the vengeance awaiting "rats and dogs".
"It's over. The issue has been decided," Gaddafi said. "We are coming tonight ... We will find you in your closets.
"We will have no mercy and no pity."
Residents said the Libyan air force unleashed three air raids on the city of 670,000 on Thursday and there was fierce fighting along the Mediterranean coastal highway.
Ten of the Council's 15 member states voted in favour of the resolution, while Russia, China and Germany were among the five that abstained. The resolution was co-sponsored by France, Britain, Lebanon and the United States.
Apart from military action, it expands sanctions against Gaddafi and associates. Among firms whose assets it orders frozen are the Libyan National Oil Corp and the central bank.
U.S. President Barack Obama called his British and French counterparts David Cameron and Nicolas Sarkozy and agreed to coordinate closely on their next steps.
Libya said the resolution, which also demands a ceasefire by government forces, was not worth the paper it was written on.
Rebel National Council head Mustafa Abdel Jalil told Al Jazeera television air strikes, beyond the no-fly zone, were essential to stop Gaddafi.
"We stand on firm ground. We will not be intimidated by these lies and claims... We will not settle for anything but liberation from this regime."
Some in the Arab world sense a Gaddafi victory could turn the tide in the region against pro-democracy movements that have unseated autocrats in Tunisia and Egypt and inspired mass protests in Bahrain, Yemen and elsewhere.
Gaddafi's Defence Ministry warned of swift retaliation, even beyond Libyan frontiers, against hostile action.
"Any foreign military act against Libya will expose all air and maritime traffic in the Mediterranean Sea to danger and civilian and military (facilities) will become targets of Libya's counter-attack," the ministry said in a statement.
Foreign military action could include no-fly and no-drive zones, a maritime exclusion zone, jamming army communications and intelligence help. Air strikes would almost certainly be launched to knock out Libyan radar and air defences.
An Italian government source told Reuters Italy was ready to make its military bases available. The airbase at Sigonella in Sicily, which provides logistical support for the United States Sixth Fleet, is one of the closest NATO bases to Libya.
The U.N. resolution followed a sharp shift in tone by the United States, which had resisted calls to military action. Diplomats said Washington's change of mind was influenced by an appeal to action by the Arab League.
"Mission creep" worries some. Western powers, chastened by protracted wars in Afghanistan and Iraq, would be wary of getting drawn into any ground action in Libya.
Germany abstained on the U.N. resolution, saying it saw "considerable dangers and risks" and that German troops would not take part in military action.
Rebels have retreated over the last two weeks as Gaddafi has brought air power and heavy armour to bear.
Residential areas of Ajdabiyah, a strategic town on the coast road to Benghazi, were the scene of heavy fighting on Thursday and around 30 people were killed, Al Arabiya reported.
On the approaches to Ajdabiyah, burned-out cars lay by the roadside and government forces showed the foreign media artillery, tanks and mobile rocket launchers -- much heavier weapons than those used by the rebels.
In Libya's third city Misrata, 200 km (130 miles) east of Tripoli, rebels and residents said they were preparing for a new attack by government troops.