Hungry men wait for bread and water to be thrown to them while waiting to enter Tunisia after fleeing Libya. Credit:Getty Images Mr Cameron told MPs that Britain and its allies were considering using fighter jets to impose a no-fly zone over Libya, patrolling and shooting down Libyan aircraft ordered to attack protesters. The Pentagon announced that the Americans had begun "repositioning forces" around Libya to provide "flexibility". The French also announced that they would back a possible military intervention with Nato partners. The warnings were sounded after Colonel Gaddafi was accused of ordering Libyan aircraft to attack a radio station being used by rebels in the city of Benghazi.

An arms depot being used by anti-government forces was also blown up in the town of Ajdabiya, 160 kilometres further south. Despite a promise in 2003 to give up weapons of mass destruction, Colonel Gaddafi is thought to have retained as much as 14 tonnes of the chemicals required to create mustard gas. The stocks are said to be stored in secret secure facilities in the Libyan desert. The chemicals would need to be mixed and loaded into shells before they could be used as weapons, but are "still a concern", a senior British government source said. "We want to make sure they're destroyed." If there are just a few air strikes his loyalists will leave him and his time will be numbered in hours. Otherwise he could survive for a long time and there could be terrible bloodshed

The disclosure came after a Gaddafi spokesman was said to have warned that there would be hundreds of thousands of deaths if the country descended into full-blown civil war. Saif Gaddafi, the dictator's son and heir apparent, was yesterday pictured brandishing an assault rifle, rallying supporters and pledging to "send weapons" to loyalists. Militias controlled by another of Colonel Gaddafi's sons were also massing on the outskirts of a rebel-held city. If the no-fly zone is agreed on, experts believe that Western governments may launch bombing raids on Gaddafi forces if he continues to attack protesters. Libyan opponents of Colonel Gaddafi are calling for Nato air strikes, amid growing fears that they are too weak to overwhelm his still-powerful military on their own or to defend liberated cities from attack.

Mustapha Gheriani, a spokesman for an organising committee of lawyers, judges and professionals in Benghazi, the leading city of the revolution, said: "We can't protect ourselves at the moment from tanks and aircraft, let alone organise a march on Tripoli to topple Gaddafi. "If there are just a few air strikes his loyalists will leave him and his time will be numbered in hours. Otherwise he could survive for a long time and there could be terrible bloodshed." Mr Cameron announced that the vast majority of Britons had been evacuated from Libya and that the evacuation of foreign nationals would be largely complete by today. The end of the evacuation effort has coincided with a meeting of senior Western politicians to begin the "next phase" of action against the Gaddafi regime. On Sunday, Britain announced emergency plans to freeze the regime's assets in London. The European Union will impose wide-ranging sanctions against Colonel Gaddafi and the Libyan government this week. Mr Cameron said: "If Colonel Gaddafi uses military force against his own people, the world cannot stand by. That is why we should be looking at a no-fly zone."

No-fly zones have previously been imposed over Iraq and Bosnia to prevent rogue regimes using air power against civilians. General Sir David Richards, the Chief of the Defence Staff, has been asked to draw up options for British military operations in Libya. Any British involvement in a no-fly operation could see Tornadoes and Typhoons flying from RAF Akrotiri in Cyprus. The Libyan air force is equipped with French-built Mirage fighter-bombers, but British planners are more concerned about the regime's military helicopters, which include Soviet-made Mil Mi-24 gunships. Reports from Libya say such helicopters have been deployed against opposition forces, killing dozens of civilians. Sources said General Richards's military options paper would also look at British ground operations. Those were likely to be contingency plans to deal with the extraction of RAF pilots in the event of planes crashing or being shot down. Another option would be giving weapons and other support to groups inside Libya.

Mr Cameron said Colonel Gaddafi's departure was Britain's "highest priority", adding: "If helping the opposition would somehow bring that about, it is certainly something we should be considering." Since the Libyan crisis began, the coalition has faced repeated criticism over the decision last year to decommission HMS Ark Royal and the Royal Navy's Harrier jets, leaving Britain without a functioning aircraft carrier. Liam Fox, the Defence Secretary, insisted that such criticism was a "red herring" because the base in Cyprus meant Britain could still operate jets over Libya if required. He said: "There has been no need for us to have a carrier, there has been no need for us to use fast jets, but we have the ability to use them if required." The Pentagon is believed to be considering moving a US aircraft carrier, the USS Enterprise, from the Red Sea into the Mediterranean to take up a position off Libya.

The USS Kearsage, an amphibious assault ship, could also be redeployed. "We're repositioning forces to provide for flexibility once decisions are made," said a Pentagon spokesman. Yesterday, reports from Libya suggested that Colonel Gaddafi - and forces still loyal to him - were preparing to attack rebels and protesters in west of the country. In an interview with US television network ABC News, the defiant dictator said: "All my people love me. They would die to protect me." Witnesses in Misrata, a city of 500,000 people to the east of Tripoli, and Zawiyah, a strategic refinery town to the west of the capital, said government forces were mounting or preparing attacks. A resident of Zawiyah, named Ibrahim, said: "We are expecting attacks at any moment by brigades belonging to [Colonel Gaddafi's son] Khamis. They are on the outskirts of the town."

The US Treasury Department announced that it has frozen at least $30 billion in Libyan government assets under US jurisdiction. "This is the largest blocking under any sanctions program ever," a spokesman said. Loading The Telegraph, London