The United States' highest ranking military officer has given the most explicit assessment yet of Washington's options to stem the bloody conflict in Syria.
But the chairman of the joint chiefs of staff, General Martin Dempsey, warned that any military intervention would be costly and uncertain. And he said that once the US took action, deeper involvement would be hard to avoid.
It is outlining the escalation of potential options to be considered by the administration on how to support the rebels in Syria … The key thing I think here is what is the military judgment as to what is possible, what are the costs and benefits of these things, and then what is the political decision that the administration will make.
General Dempsey assessed the risks and benefits of five military options: Arming and training opposition troops that would cost $500m a year; then there is limited air strikes, establishing a no-fly zone, creating buffer zones inside Syria, and controlling the government's chemical arms.
These last four options would each cost around $1bn a month.
General Dempsey acknowledged that any such action would strengthen the opposition and put pressure on Syrian President Bashar al-Assad.
But he warned: "The decision to use force is not one that any of us takes lightly. It is no less than an act of war."
Even so, the US signed off on the shipment of small arms and other weaponry to Syria's opposition just last week. It was part of a covert CIA operation approved by US President Barack Obama.
When Syria's armed insurgency began, defectors from the country's staunchly secular army formed the backbone of the opposition.
Two years later, Syria's rebels have a more Islamist complexion. The Free Syrian Army is the most well-known. It was founded by army deserters. But it is not unified, and is more an umbrella for different brigades across Syria, some with very different ideologies.
Among the more notorious fighters in Syria's war, is Jabhat al-Nusra or the Nusra Front. They are a breakaway from Al Qaeda in Iraq, but have fighters from across the region.
The US considers the Nusra Front a terrorist organisation, as it does Ahrar al-Sham, one of Syria's biggest and most organised fighting factions.
Ahrar al-Sham has been called 'Jihadi' brigade but its objectives are very different to the Nusra Front - not least because it is predominantly made up of Syrians.
So what constitutes Syria's opposition? Who would the US be dealing with? How would US intervention shape the outcome to the Syrian conflict? And what are the risks, costs and consequences of military intervention?
Inside Story, with presenter Mike Hanna, is joined by guests: Kurt Volker, the executive director of the McCain Institute and former US permanent representative to NATO; Khaled Saleh, a spokesman for the Syrian National Coalition, and Mark Perry, a military, intelligence and foreign policy analyst.
"The hesitation that we have seen from the Obama administration has echoed ... the hesitation that we see in France and the UK as well. At the end the people are getting killed ... and I think the US understands that there is a void, and if the US and its allies are not willing to move in to fill that void, then we are going allow extremist to move in .... All I know if we leave the situation as it is, it's just going to get worse by the day, we need the international [community] to get involved, we need the US to take a more of a leadership position on this issue."
- Khaled Saleh, a spokesman for the Syrian National Coalition