US officials say they will give rebels in Syria "direct military aid". Experts examine the impact that the US decision will have on the conflict and on the region.

US officials said that they believe government forces in Syria have used chemical weapons against the opposition rebels.

PJ Crowley, professor at George Washington University's Institute of Public Diplomacy and Global Communication

Light arms are not enough

The White House concluded that the Assad regime employed small amounts of chemical weapons. Having drawn that red line, something had to change.

The decision also reflects a dire shift in momentum on the battlefield. With Iran increasing its support, Hezbollah "all in", and little prospect of a political settlement, weapons represent the least bad among various options.

What will happen next? That depends on what the increased support actually is and whether the opposition is able to use it to greater effect. US ground troops have been ruled out.

PJ Crowley Professor at Institute of Public Diplomacy and Global Communication

Former US assistant secretary of state for public affairs, 2009-11

A no-fly zone, while possible, would make the US a direct combatant in the civil war, a step for which there is limited public support.

Light arms are not enough. Anti-aircraft missiles could migrate out of Syria and threaten commercial aviation.

Something in the middle, possibly involving anti-tank weapons, is likely.

Ultimately this looks more and more like the kind of proxy war the US waged during the Cold War.

The idea is to raise the cost for your adversaries, including Russia, Iran and Hezbollah.

It can succeed. It can backfire. One thing is for sure - it won't end soon.

Image caption A rebel fighter takes a break from the battles

David Rieff, author of A Bed For The Night: Humanitarianism in Crisis

It is impossible to know how the ill-conceived and, by all accounts, half-hearted decision by the Obama administration to provide some advanced weapons to those elements of the Syrian insurgency that Washington believes it can safely support will actually turn out.

Much depends on the quality and quantity of weapons the US is planning to provide

Despite recent victories by Syrian government and Hezbollah forces in Qusayr and in the suburbs of Damascus, the situation on the battlefield remains fluid with both the Assad regime and the rebels each still firmly convinced they are going to prevail.

Much depends on the quality and quantity of weapons the US is planning to provide and how many trainers will be deployed to ensure they are used to maximum effect.

What is clear is that, having insisted for more than two years that it was inevitable that Assad would fall, the Obama administration now realises its adolescent progress narrative about Syria as one of the last dominoes of the Arab Spring is so much liberal internationalist, human-rights-ist wishful thinking, and that outside military help for the Syrian rebellion is necessary not to ensure its victory but rather to stave off its defeat.

Why both liberal interventionists and neo-conservatives are so persuaded that overthrowing Assad and inflicting a defeat on Hezbollah is both a moral and a geo-strategic imperative, even if the effect is, as in Iraq, to evict Christianity from one of its homelands and make Syria safer for al-Qaeda, is a mystery to me.

But this, it seems, is what the consensus has become.

Elizabeth O'Bagy, senior research analyst at the Institute for the Study of War

Additional options must be considered that would limit the human cost

The proposed light arms and ammunition will be just enough to sustain the defensive capabilities of the opposition and may prevent an all-out defeat.

But it falls short of providing the type of support needed to protect civilians from the regime.

Given the involvement of Hezbollah fighters in the battles and the new higher confidence being displayed by the regime in its advance on Aleppo, the military assistance being offered will not be enough to shift the momentum.

Frankly, any sort of programme that doesn't provide anti-aircraft capability will not help in the protection of civilians. It will do little to alleviate their suffering under the threat of aerial bombardment.

Additional options must be considered that would limit the human cost and mitigate the risks to regional stability.

A combined strategy that would also help ground the Syrian air force must be part of any policy to shape the direction of the Syrian conflict.

Image caption Rebel fighters train in Syria

Joshua Landis, University of Oklahoma's Center for Middle East Studies

Will Obama be content if the Free Syrian Army can take Aleppo and the north of Syria, dividing the country in two?

Obama has started down a slippery slope

Will he decide that the rebels should take Damascus as well, pushing the regime and the Alawite religious group, which predominates within the regime, back toward the western coastland?

Or will Obama decide to back the rebels with enough firepower to destroy the regime altogether and disarm the Alawite villages that are clustered along the coastal mountains?

Now that the US has decided to champion the opposition militarily, it must set out goals.

The choices are dividing the country in two, which would simply confirm the present status quo, more or less; dividing the country into three, following the ethnic lines of the major combatant groups; or keeping the country one. This would mean arming the Sunni opposition with enough weapons to conquer both the Alawites and Kurds.

The US must also take responsibility for ensuring that ethnic cleansing of Syria's minorities is not carried out by Sunni militias, which are bound to be angry and vengeful after the terrible beating they have taken at the hands of the Alawite-dominated Syrian Army.

Only an international peace-keeping force can guarantee against unnecessary bloodshed if Obama hopes to arm the Sunni militias for total victory.

Obama has started down a slippery slope.

He owes both the American and Syrian people a clear statement about what he sees as Syria's future borders, what kind of government he hopes to see in the future and how he will carry it out.