Libyan dictator Muammar Gaddafi last night threatened retaliatory attacks against passenger aircraft in the Mediterranean if foreign countries made air strikes against his country.
The warning came as the United States said it would back a United Nations resolution for military action to protect civilians against Gaddafi's forces.
After deliberating for weeks over what to do about Gaddafi, the UN acted with sudden speed and passed the resolution as it became clear the dictator would try to finally put a brutal end to the month-long rebellion against his rule, especially in the opposition-held city of Benghazi.
Early this morning (New Zealand time), British Prime Minister David Cameron told the House of Commons that Royal Air Force Tornados and Typhoons were being readied to enforce a no-fly zone over Libya.
He said the decision to deploy the armed forces was based on three considerations - there was a demonstrable need, there was regional support from the Arab League and others, and the action was legal.
He said the aim was not to choose the government of Libya but to save lives by preventing "a brutal attack using air, land and sea forces" by Gaddafi on Benghazi.
France and Nato were holding emergency meetings early this morning.
At the same time, reports were coming in that Gaddafi forces had stepped up their attack on the rebel-held city of Misrata, 200km east of the capital Tripoli and across the Gulf of Sirte from Benghazi.
"They are bombing everything, the houses, the centre of the city," insurgent Saadoun told Reuters by phone from the city, the last big rebel stronghold in western Libya.
"It's the heaviest bombardment I have seen so far."
The sound of heavy artillery could be heard in the background.
The attack began hours after the UN Security Council passed a resolution endorsing the no-fly zone and military attacks on Gaddafi's forces to protect civilians.
"We believe they [Gaddafi's forces] want to enter the city at any cost before the international community starts implementing the UN resolution," said Saadoun.
"On behalf of all the people of Misrata, the women, the children and the elderly, we call on the international community to do something before it's too late. They must act now," he said.
Another insurgent who gave his name only as Mohammed said government tanks were advancing towards the centre of the city and the rebels were trying to resist them.
The UN Security Council passed its resolution after Gaddafi urged rebels in Benghazi to surrender, and backed his call with threats.
"We are coming tonight ... There won't be any mercy."
Speaking in an interview with Portuguese television broadcast just before the UN vote, Gaddafi pledged to respond harshly to UN-sponsored attacks.
"If the world is crazy," he said, "we will be crazy, too."
The Security Council responded with the resolution authorising the world to take "all necessary measures" to prevent attacks on Libyan civilians by the Gaddafi regime.
It imposed the no-fly zone over Libya and authorised force short of a ground offensive to protect the people from the dictator's forces.
The Libyan Defence Ministry delivered its warning of retaliation as it became clear the UN resolution would be passed with Americansupport.
"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," it said.
The Security Council resolution was passed 10-0 but split the leading powers, with China, Russia, Germany, India and Brazil not voting.
The UN resolution
* Immediate ceasefire.
* End to violence against civilians.
* Libyan authorities to allow humanitarian assistance.
* UN member states to take all necessary measures to protect civilians and civilian populated areas under threat of attack in the country, including Benghazi.
* No-fly zone over Libya.
* Foreign occupation force.