Muammar Gaddafi's government said it was declaring a unilateral ceasefire in its offensive to crush Libya's revolt, as Western warplanes prepared to attack his forces.

"We decided on an immediate ceasefire and on an immediate stop to all military operations," Foreign Minister Moussa Koussa told reporters in Tripoli on Friday, after the U.N. Security Council passed a resolution.

He called for dialogue with all sides. Gaddafi had vowed to show "no mercy, no pity" on Thursday, and rebels pleaded for foreign aid before time ran out. They said the city of Misrata was being pounded by government forces on Friday morning.

People in Misrata said the rebel-held western city was under heavy bombardment by Gaddafi's forces on Friday.

"They are bombing everything, houses, mosques and even ambulances," Gemal, a rebel spokesman, told Reuters by phone from the last big rebel stronghold in the west.

Another rebel named Saadoun said: "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."

A fighter named Mohammed said tanks were advancing on the city centre. "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.

The reports could not be independently confirmed. Authorities were preventing Tripoli-based foreign journalists from reporting freely.

"NO-FLY ZONE

France said it was cautious about the ceasefire announcement and that the "threat on the ground has not changed".

Western officials said military action could include France, Britain, the United States and one or more Arab countries.

"Britain will deploy Tornadoes and Typhoons as well as air-to-air refuelling and surveillance aircraft," Prime Minister David Cameron told parliament.

"Preparations to deploy these aircraft have already started and in the coming hours they will move to airbases from where they can start to take the necessary action."

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. France is to host international talks on Saturday to discuss the action.

"THREAT"

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 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.

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 Gaddafi's 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.

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 authorised "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 centres. Gaddafi's ground troops are advancing from the west along the main coast road towards 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 on Thursday warned Benghazi 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."

AIR STRIKES

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.

European air traffic control organisation Eurocontrol said Malta had told it that Tripoli air traffic control was not accepting aircraft into Libyan airspace "until further notice".

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.

Germany said it saw "considerable dangers and risks". 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 authorise invasion, and said he did not want any side "to go too far".

Gaddafi would be guilty of war crimes if he carries out a threat to attack civilians in Benghazi, the International Criminal Court's prosecutor Luis Moreno-Ocampo said.

Oil prices fell after the ceasefire announcement. Brent crude was 49 cents lower at $114.41 by 1308 GMT.

Agencies