Analysis: Options for military intervention in Syria
As the civilian death toll mounts in Syria, is the international debate reaching a tipping point?
For all the unease about direct outside military intervention, will there come a moment when humanitarian concerns and the fear of a wider regional crisis shift the balance, making action inevitable?
For the moment, that does not seem to be the case.
Indeed, since the outset of the Syria crisis in March 2011, there has been little appetite for outside military intervention. This has been based on two assessments.
Firstly, that this would be no simple military option: the situation on the ground in Syria is in many ways very different from that in, for example, Libya - the opposition is much more divided, the government's security forces are much stronger, and Syria's air defences are more effective.
Secondly, there has been a view that the implications of toppling President Bashar al-Assad could prompt a much wider wave of instability in the region. Unlike Libya, Syria - both politically and geographically - is a central player in the Arab world, and sectarianism and instability there could threaten both Lebanon and Iraq.
Then, of course, there is the fundamental legal problem. Constrained by Russian and Chinese vetoes at the UN Security Council, there is no possibility of getting a resolution to authorise force.
That has not always mattered in the past. Nato troops went into Kosovo, after all, to halt systematic abuses by Serbian forces. But the absence of legal authorisation certainly precludes action when there is little enthusiasm for it in the first place.
So what are we to make of calls from senior Republican politicians in the US, like Senator John McCain, urging air strikes against Syrian security forces?
Joshua Landis, director of the Centre for Middle East Studies at the University of Oklahoma, says: "Despite the growing chorus of politicians calling for US leadership in Syria, the Obama administration is adamant that Washington should not take the lead, but follow regional partners, Saudi Arabia and Turkey."
Mr Landis argues the simple fact is that the Obama administration sees no strong reason to intervene.
"US officials are unanimous in arguing that the Assad regime is doomed and can only hang on for a limited time, with or without increased US support for the Syrian opposition. I think they are right in this analysis.
"This means that the US has no compelling national security interest in jumping into the Syrian civil war that is emerging. The regime's days are numbered."
Much of the debate on outside intervention is vague. It confuses and makes false distinctions between the different options and to a large extent glosses over many of the fundamental problems facing them all.
Assistance and relief
The main thrust of any external action would be essentially humanitarian in nature, a response to the growing plight of civilians in Syrian towns and cities who are under bombardment by government forces.
Efforts could also be made to bring assistance to displaced refugees who have moved towards Syria's frontiers with Turkey and Lebanon. Three related measures are being discussed.
Suggested first by the then French Foreign Minister Alain Juppe last year, the idea would be to establish short corridors into Syrian territory through which humanitarian supplies could be delivered.
The establishment of safe areas within Syrian territory is an idea that has been broached by the Turkish Foreign Minister, Ahmet Davutoglu. Such havens would be in border areas, acting as a place of safety where refugees could gather, be fed and sheltered, and so on.
Often discussed in relation to both of the above, the suggestion is that Western air power could help ensure the safety of the zones or corridors.
In itself, air power would not halt the fighting. It is not the Syrian air force that is primarily involved in offensives on opposition strongholds - although activists say jets and helicopters have been used to carry out reconnaissance and occasionally air strikes - but the government's ground forces.
But a discussion of air power underscores that unless the Syrian authorities agree to allow humanitarian access, any safe zones or corridors would first have to be established by force and then defended by force.
The horror of Srebrenica in the Balkans showed what can happen if there is no will to defend a safe zone once created.
The key point here is that even the options directed primarily at humanitarian relief require significant military elements too. They involve seizing and holding bits of Syrian territory and a willingness to take on Syrian forces if necessary.
Air power would be crucial - though Western warplanes would have to contend with Syria's reasonably sophisticated air defences. Boots would almost certainly be needed on the ground too. These are not "military lite" options.
Changing the balance of power
These options seek to accelerate the processes already at work in Syria both by strengthening the opposition forces and thus seeking to increase the pressure on the Syrian authorities.
Again, a range of strategies is available.
Logistical support for armed rebel groups
This has probably been under way for some time. The idea is to provide medical supplies and non-lethal equipment such as radios to make the opposition more effective.
For some, this is seen as the thin end of the wedge, leading to the arming of rebel forces. This is certainly what happened in Libya.
The aim here would be to limit weaponry and munitions going to the Syrian government.
In the absence of UN Security Council action, this would rest on shaky legal ground. It might also mean being willing to halt Russian shipping, since it is Moscow that remains the Assad regime's principle armourer.
Arming the rebels
Both Qatar and Saudi Arabia have voiced their support for arming the opposition forces in Syria. There are strong indications that over recent weeks, the quality and quantity of weaponry going to the Syrian opposition has improved, as has their effectiveness.
Pressuring the Syrian military
Simon Henderson, senior fellow at the Washington Institute for Near East Policy, wonders if arming the opposition "is necessarily the best tactic", and getting the Syrian army to flip might be a better way of getting rid of President Assad.
"Pressure needs to be put on different division commanders," he argues.
"The US can no doubt identify the commanders and possibly communicate with them - it did this sort of thing during the invasion of Iraq."
Indeed, there have been persistent reports of the US flying drones over the country to gather evidence of humanitarian abuses.
"Of course," he notes, the risk is that "this might only bring about a new military-led regime".
Punitive air attacks
When the offensive against Homs was at its height, the US very publicly released satellite photos showing Syrian artillery batteries and rocket launchers attacking the city.
There were two messages here - one was that the world was watching and documenting what was happening; the second was perhaps a potential threat - what can be seen from the air can be hit from the air.
But as yet there is simply no appetite in Washington to engage in another military conflict in the Middle East.
Any attack against Syria would have to be on a much larger scale compared to the military operations launched against Libya.
Indeed, initial US military assessments suggest that a protracted campaign against Syria's integrated air defences, due to their location, could lead to serious civilian loss of life. For now, such an operation is simply not on President Barack Obama's agenda.
Intervention: the wider debate
An active discussion about the merits or pitfalls of intervention is nonetheless being waged in both Arab and Western capitals. The crisis in Syria is so serious and the stakes are so high that nobody wants to rule out any option. Much, of course, depends upon how things develop.
A central concern in the debate relates to weapons supplies and their impact, not so much on the struggle between the Assad regime and the opposition, but on the Syria that eventually emerges from this crisis.
"There are many divisions among the Syrian opposition, but all the militant groups want to bring down the regime," Joshua Landis says. "The divisions will not minimise the impact of outside weapons supplies, but they will inhibit any stable government from replacing the present Syrian Army."
So could a further militarisation of the conflict lead to prolonged civil war should the Assad regime collapse?
"Yes," Mr Landis answers. "The sectarian and ethnic divisions in Syria are a recipe for prolonged struggle as is the case in Iraq, Palestine-Israel, and Lebanon.
"Decapitating the Syrian regime, through outside intervention," he believes, will provide no guarantee of ending the killing.
"On the contrary, it could well accelerate the killing if there is no unified leadership which can assume control of Syria and no militia that can impose some order in the place of the Syrian national army. If the sort of civil war that Iraq experienced breaks out, the killing could well spike."
Steven Heydemann of the United States Institute of Peace shares these concerns, but comes to a rather different conclusion.
"The further militarisation of the crisis is inevitable," he says.
"As the regime escalates its use of force against civilians, the armed opposition will expand, and will come to play an even more central role in the uprising than it has to date.
"Arms are flowing into Syria across all of its borders - to varying degrees - and the unwillingness of the West or Turkey to endorse the arming of the opposition will not affect this trend," he adds.
"The single biggest danger of militarisation", he warns, "is that it empowers and gives legitimacy to the armed opposition and contributes to the marginalisation of the political opposition, which is perceived as ineffective in providing protection to civilians who bear the brunt of regime violence.
"Increasingly, it is the men with guns who wield power in areas outside of government control, with very troubling implications for Syria's future."
Policy, though, inevitably changes over time. The drivers will be events on the ground inside Syria and the reaction to these events from outside the country.
Soner Cagaptay, a Turkey specialist also at the Washington Institute for Near East Policy, says that the evolution of Ankara's approach is a case in point.
"Initially, Turkey sought to build UN-led action against President Assad. When that failed, Turkey turned to the Arab League and Friends of Syria group to build internationally sanctioned policy against Damascus," he says.
"At the same time, Ankara started to host and coach the Syrian opposition. Now, Ankara's policy is entering a third phase, namely calling for humanitarian access for the civilians. This suggests getting relief to the civilians.
"But", he adds, "if that policy, too, fails to end the crackdown, the next step will likely be a move into phase four, namely actively arming the opposition in an effort to create a more robust resistance and protection for civilians against Assad's crackdown.
"The final step in Ankara's Syria policy, if this measure too fails to deliver a concrete victory, against Assad would be calling for a no-fly zone inside Syria to protect civilians."
That, as discussed above, could be a prelude to some broader outside military intervention.
But there is a growing pessimism about what external actors can do. So far, diplomatic efforts have delivered little.
The so-called Friends of Syria - perhaps as accurately dubbed "the enemies of President Assad" - have had only modest success in encouraging the Syrian opposition to become more united.
The plan by Syria special envoy Kofi Annan appears dead in the water. And proposals for a new diplomatic initiative involving Russia again seem to offer only limited hope of progress.
Perhaps more encouraging for President Assad's opponents is the impact of economic sanctions.
Joshua Landis says sanctions are devastating the Syrian economy and have led to sharp falls in the value of the Syrian pound.
"They are encouraging some people to leave the country and others to take up arms. It will not be long before hunger and deprivation begin playing an important role in the disturbances."
Furthermore, Mr Landis says, the sanctions "are weakening the government's ability to reassure businessmen that the regime can provide for them".
Over time, this will serve to detach key groups from their support for the regime.
But economic sanctions require considerable time to take effect and are a blunt tool; harming the country's economy inevitably hurts the ordinary man or woman in the street.
So with no immediate answers on either the economic or diplomatic fronts, each new massacre revives the calls for some kind of military action.
On one side of the argument, there is the fear that without a clear political framework for Syria's future, the toppling of President Assad could simply precipitate the country's fall into bloody chaos. Thousands more lives could be lost.
Outside intervention might sweep away the regime, leaving a situation like post-war Iraq, where sectarian violence dominated and Western troops were drawn into a quagmire.
Others argue the seeds of this catastrophic future can already be seen.
As the violence in Syria increases, so does the risk of the crisis spreading to neighbouring Lebanon and perhaps from there turning into a regional conflagration, maybe drawing in Israel or even Turkey.
Better, according to this argument, to act soon to dismantle the Syrian regime before the contagion spreads. Unpalatable intervention may be, but it is even worse, in this view, to stand by and watch the slaughter of innocents.
What is clear is that there are no easy options.