|The British government is also considering arming opposition groups in Libya, Cameron said [Reuters]
David Cameron, the British prime minister, has said the international community cannot let Libyan leader Muammar Gaddafi "murder" his own people, as he justified considerations for a no-fly zone over the riot-torn country.
"It's not acceptable that Colonel Gaddafi can be murdering his own people, using aeroplanes and helicopters gunships ... and we have to plan now to make sure that if it happens we can do something to stop that," he said on Tuesday.
"If he starts taking that sort of action we might need to have a no-fly zone in place very quickly."
His comments come as Catherine Ashton, the European Union's foreign policy chief meets Anders Fogh Rasmussen, the Nato secretary-general in Brussels, the Belgian capital, over the situation in Libya.
Cameron said he had asked the ministry of defence to work with its allies over plans for a no-fly zone over Libya, a move that would see fighter jets used to patrol and shoot down Libyan aircraft ordered to attack protesters.
He added that the government would consider arming opposition groups fighting in Libya.
"If helping the opposition would somehow bring that about it is certainly something we should be considering," he said.
However, a senior US military official warned on Tuesday that establishing a no-fly zone in Libya would be a "challenging" military operation.
"My military opinion is that it would be challenging," General James Mattis, commander of US Central Command, told a Senate hearing. "You would have to remove air defence capabilty in order to establish a no-fly zone, so no illusions here. It would be a military operations - it wouldn't be just telling people not to fly airplanes."
France urges UN mandate
But the US said on Monday it was actively considering such plans, with Hillary Clinton, the US-secretary of state, saying "all options are on the table".
However France has said military intervention in Libya could only go ahead with a clear United Nations mandate.
"At the moment I speak, no military intervention is planned," Alain Juppe, the French foreign minister said on Tuesday.
"Different options can be assessed, notably a no-fly zone. But let me put it clearly here - no intervention will happen without a clear UN Security council mandate".
Barak Seener, a research fellow at the Royal United Services Institute, told Al Jazeera that any UN resolution backing a no-fly zone "would have to demand that the no-fly zone is not open ended and subject to review at certain intervals".
He said as most of the atrocities are taking place on the ground, such a plan could lead to a no-drive zone, or a no-sail zone, and so clear parameters would be needed.
John Rees from the London-based Stop the War Coalition has said such military intervention would be a "prelude to a new war" and a "classic foreign policy blunder".
In an interview with the BBC he said Egypt and Tunisia had proved that people were capable of overthrowing their governments without the help of Western nations.
He added that Libyans were capable of toppling Gaddafi's regime alone, saying large sections of the military had already defected.
Talks over military intervention come after the United Nations security council backed a resolution condemning Gaddafi's actions, imposing travel bans and asset freezes on key government figures.
The European Union has also approved its own sanctions on Libya, including an arms embargo and travel bans, and a number of nations, including Britain, the US, Germany, Canada, Switzerland and Austria have announced their own asset freezes.
Source: Al Jazeera and agencies