David Cameron warns Col Gaddafi to face consequences
Libyan leader Col Gaddafi has broken his own ceasefire and will now face the consequences of his actions, Prime Minister David Cameron has said.
Speaking after a summit of world leaders in Paris earlier, Mr Cameron said "the time for action has come".
He is now hosting a meeting of the government's emergency management committee "Cobra" in Downing Street.
In Libya, a French warplane has fired the first shots as part of the no-fly zone imposed by the United Nations.
French defence chiefs have confirmed about 20 warplanes are involved in operations over Libya, with one opening fire on a Libyan military vehicle.
Mr Cameron said the meeting in Paris was successful, and stressed that Arab countries had played a part.
"What is absolutely clear today [Saturday] is that Col Gaddafi has broken his word, has broken the ceasefire and continues to slaughter his own civilians," he said in the French capital.
"This has to stop. We have to make it stop. I think it is vitally important that action takes place. That action takes place urgently."
He continued: "It is better to take this action than to risk the consequences of inaction, which is a further slaughter of civilians, and this dictator completely flouting the United Nations and its will."
Asked if military action would now go ahead, he said: "Gaddafi has made this happen. He has lied to the international community, he has promised a ceasefire, he has broken that ceasefire, he continues to brutalise his people, and so the time for action has come."
Despite the Libyan regime declaring a ceasefire, offensives are reportedly continuing in the rebel-held city of Benghazi.
There are reports that the city is under attack, and tanks have been seen on the streets.
Libyan officials have dismissed these reports as untrue, and said it would abide by the UN resolution and international observers could enter the country to verify the situation.
A Cobra meeting was also held earlier on Saturday, chaired by Deputy Prime Minister Nick Clegg.
The agenda was dominated by Libya but a spokeswoman said there were also discussions on events in Yemen and Bahrain.
Meanwhile the government's decision to pursue a no-fly zone was backed by Labour leader Ed Miliband.
Addressing a party conference in Scotland, he said: "We know in our hearts and in our heads when we see Colonel Gaddafi murdering his own people, it is right to take this action."
Shadow foreign secretary Douglas Alexander said the agreement in Paris was a "powerful statement of unity" in the face of "slaughter".
He told the BBC: "The urgency of the response needs to match the urgency of the threat and that is why it is important the Gaddafi regime recognises the full force of the international community's will."
The commander in charge of planning for the no-fly zone will be US Adm Samuel Locklear, the BBC's Mark Urban has learned.
Two RAF Tornado aircraft were seen taking off from RAF Lossiemouth in Moray and landing at RAF Marham in Norfolk. The planes are now reportedly equipped with long-range fuel tanks.
Neither the Ministry of Defence nor Downing Street have yet confirmed whether any British aircraft have left to join the no-fly zone operation.
But the Canadian military said the CF-18 planes which landed at Prestwick Airport in Ayrshire earlier on Saturday had now left, bound for Italy to assist the UN-backed mission.
The UN resolution imposes a ban on all flights in Libyan airspace, excluding aid flights, and authorises member states to "take all necessary measures" to "protect civilians and civilian populated areas under threat of attack" short of putting an "occupation force" on the ground.
It would permit air strikes on Libyan ground troops or allow attacks on Libyan war ships if they were attacking civilians.
The Tornado GR4 fighter jet, equipped with precision weapons, is among the first military assets the UK could use to defend a no-fly zone.
The planes are stationed at RAF Marham and RAF Lossiemouth, though it is not yet clear which military base they would ultimately fly from.
Options include bases in southern France, southern Italy or RAF Akrotiri in Cyprus, or - with permission - Malta.
Typhoon warplanes, based at RAF Coningsby and RAF Leuchars, are most likely to be used in an air-to-air combat role. UK reconnaissance and refuelling planes are also being deployed.
MPs are to get the chance to vote on the UK's potential involvement at the end of a Commons debate on Monday.