By Maria Golovnina and Patrick Worsnip
TRIPOLI/UNITED NATIONS (Reuters) - The United Nations authorized Western-led attacks on Muammar Gaddafi's forces, as he vowed to crush Libya's revolt with "no mercy, no pity" and rebels pleaded for military aid before time runs out.
French sources said action could follow in hours, and could include France, Britain, possibly the United States and one or more Arab countries.
A U.S. official said no immediate U.S. action was expected. Gulf state Qatar said it would take part but it was unclear whether that meant military help, while Denmark said it planned to contribute warplanes.
People in Misrata said the rebel-held western Libyan city was being pounded by Gaddafi's forces on Friday morning.
"They are bombing everything, the houses, the center of the city," rebel Saadoun told Reuters by phone. "We believe they want to enter the city at any cost before the international community starts implementing the U.N. resolution.
"We call on the international community to do something before it's too late. They must act now."
Another fighter named Mohammed said tanks were advancing toward the center. "All the people of Misrata are desperately trying to defend the city," he said.
Four people had been killed and 70 wounded, Al Arabiya television said. A government spokesman said the military operation should be completed on Friday.
Time was also 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 fulfill 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.
Gaddafi's son Saif al-Islam said Libya was "not afraid" of the U.N. resolution, Al Arabiya said.
He said the army would surround but not enter Benghazi and "anti-terror" forces would be sent in to disarm rebel forces, Al Jazeera quoted ABC news as saying.
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 tricolors and chanting defiance of the man who has ruled for four decades.
Fireworks burst over the city and gunfire rang out.
Some had fled to the Egyptian border on Thursday but said the U.N. move had given them new hope. "It's a great development. We are so thankful," said Rajab Mohammed al-Agouri, with five children. "But we are waiting for it to be implemented. We are tired of talk."
The U.N. Security Council, meeting in emergency session, passed a resolution endorsing a no-fly zone. It also authorized "all necessary measures" -- code for military attack -- to protect civilians from Gaddafi's forces.
Libya's military airfields are mostly strung along the Mediterranean coast, as are its population centers. Gaddafi's ground troops are advancing from the west along the main coast road toward Benghazi in the east.
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 favor 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 British and French leaders David Cameron and Nicolas Sarkozy and agreed to coordinate closely on their next steps.
European air traffic control organization Eurocontrol said Malta had told it that Tripoli air traffic control was not accepting aircraft into Libyan airspace "until further notice."
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 defenses.
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 said it saw "considerable dangers and risks" and that German troops would not take part in military action. NATO member Turkey also said it opposed the operation.
Arab League chief Amr Moussa said the U.N. resolution was aimed at protecting civilians and not did not authorize invasion, and said he did not want any side "to go too far."
Rebels have retreated over the last two weeks as Gaddafi has brought air power and heavy armor to bear.
(Additional reporting by a Reuters reporter in Benghazi, Michael Georgy in Tripoli, Mariam Karouny and Tarek Amara in Tunisia, Louis Charbonneau and Patrick Worsnip at the United Nations and John Irish in Paris; writing by Andrew Roche; editing by Giles Elgood)