|The US and Britain enforced no-fly zone over Iraq following the Gulf War, without a UN resolution [GALLO/GETTY]
Britain and the United States have said they are considering plans for establishing a no-fly zone over Libya to stop government forces from firing on their own people, in moves that could echo the military intervention seen in the Balkans and Iraq during the 1990s.
Such plans could allow Western states to show their commitment for pro-democracy protesters without getting involved in combat on the ground, but the measure would be controversial for logistical, political and legal reasons.
Setting up a no-fly zone is not a simple task. Vast military resources, including hundreds of fighter jets and surveillance teams are required, along with solid parameters, rules of engagement and legal backing.
More than 200 US aircraft and dozens of British military planes and surveillance aircraft were deployed to police a no-fly zone enforced over areas of Iraq after the 1991 Gulf War, costing governments billions of dollars.
The crisis in Libya comes at a tough time for Western nations, which are suffering from major spending cuts due to spiralling national deficits and an economic downturn.
Britain's government has already slashed its defence budget, scrapping its Harrier jump jet fleet and Ark Royal aircraft carrier and shedding thousands of personnel, leading to renewed criticism that it is leaving itself unprepared for amid the pan-Arab uprisings.
Ongoing operations in Afghanistan have also left London and Washington's military resources and capabilities stretched.
"If we move additional assets, what are the consequences of that for Afghanistan, for the Persian Gulf and what other allies are prepared to work with us in some of these things?" Robert Gates, the US defence secretary said on Tuesday.
On top of that, Libya is said to have relatively sophisticated military capabilities, including an advanced air defence system comprising 18,000 members and more than 200 fighter jets.
It is also believed to hold 50 Soviet-designed SA-6 missiles, which may have the capacity to shoot down US and European jets.
The Libyan system "consists of much more modern surface-to-air missiles" than the Iraqi defences destroyed by US forces in 2003, David Deptula, a former fighter pilot told the Washington Post.
The reports have raised concerns that any foreign force entering Libya would face the prospect of combat, another complicating factor for setting up a no-fly zone.
Some analysts also suggest that one could only be implemented effectively by first destroying Libya's air defences through a bombing campaign, which could mean civilian deaths.
"What you include in a no-fly zone agreement is important," Dr David Whetham, senior lecturer at the defence studies department at Kings College in London, told Al Jazeera.
"How are you going to include third parties and are you going to stop all movement in the state? It appears that Gaddafi is bringing in foreign mercenaries, how are you going to tell the difference between those and humanitarian flights?
"You have to be clear about what you're going to do. Are you authorised to fire on Libyan aircraft or do you wait until it fires at you? Are you going to find yourself in front of the International Criminal Court because you just shot down a civilian airliner?"
Gaining legal backing for a no-fly zone in Libya could also prove tricky.
Most analysts doubt that Western nations could achieve a UN mandate for military intervention, an element the French have said is necessary for any action, but that Russia and China are likely to veto.
Barak Seener, a research fellow at the Royal United Services Institute in London, told Al Jazeera no-fly zones can go ahead without a UN resolution, finding legitimacy in existing articles instead.
"If the UN doesn't back a no-fly zone it doesn't make it illegal," he said, adding that it can be possible without explicit authorisation.
"A no-fly zone is just not allowing aircraft to come into that area of jurisdiction. So for example Gaddafi would not be able to fly in his militias from African states. He wouldn't be able to be bombing his people, he wouldn't be able to be shelling his people.
"The problem is that it’s very easy to down a rebel force [such as the one said to have taken over an airfield in Benghazi].
"Another problem is it can spiral into being a no-drive zone, or a no-sail zone. It can suck internatinal forces into Libya in an open-ended manner," he said.
Stefan Talmon, a professor of public international law at Oxford University, recently wrote that any action without the backing of the United Nations Security Council could be questioned under international law.
"The two no-fly zones over Iraq ... were based on the doctrines of ‘implicit authorization’ (United States) and ‘humanitarian intervention’ (United Kingdom). Neither of those doctrines has gained general, or even widespread, acceptance in international law," he wrote on the blog of the European Journal of International Law.
"Any unilateral action by Nato or another ‘coalition of the willing’ would thus head for a 1999 Kosovo-style scenario which might at best be described as ‘illegal but legitimate’ – the ultimate admission of defeat for any international lawyer."
Whetham adds there is a danger in setting some precedents - no one foresaw, when Nato went ahead with the Kosovo campaign, that Russia would use the same arguments 10 years later against Georgia.
There is also a strong political element for any decision over setting up a no-fly zone.
A Western coalition intervening in the affairs of a sovereign Arab nation is likely to divide international opinion and could lead to unintended outcomes. It could also be used by Gaddafi to rally support for his regime, Whetham says.
"How involved do you want to be in someone else's revolution?" he says. "We've seen this debate seen throughout the 20th century - on whether to intervene [in the affairs of a sovereign state].
"We've seen this debate seen throughout the 20th Century - on whether to intervene on a sovereign state.
"You can't give people freedom - they have to get freedom. We must surely have realised this by now.
"It's worth going back to [political philosopher] John Stuart Mill in 1859, who said that when we choose not to intervene, we are effectively choosing to side with the bigger power."
But he said international forces could help by enforcing some kind of no-fly zone that would prevent Gaddafi from flying in external power.
"While it might not create a real level playing field for those fighting for their freedom, it might at least help prevent it getting any more uneven" he said.