In co-ordinated messages yesterday, the White House and State Department said they still hoped for a political solution. But faced with the daily onslaught by Mr Assad's regime against Syrian civilians, officials dropped the administration's previous strident opposition to arming anti-regime forces. It remained unclear what, if any, role the US might play in providing such aid.
"We don't want to take actions that would contribute to the further militarisation of Syria, because that could take the country down a dangerous path," White House press secretary Jay Carney said. "But we don't rule out additional measures if the international community should wait too long and not take the kind of action that needs to be taken."
State Department spokeswoman Victoria Nuland used nearly identical language. "We don't believe that it makes sense to contribute now to the further militarisation of Syria," she said.
"What we don't want to see is the spiral of violence increase. That said, if we can't get Assad to yield to the pressure that we are all bringing to bear, we may have to consider additional measures."
The escalating daily death toll and the failure of diplomacy to end the crisis is spurring greater international interest in the possibility of providing the FSA with logistical support to hasten the collapse of the regime. Two influential US senators, including John McCain, have declared support for arming the Syrian rebels, citing Iranian and Russian material backing for the regime.
The rebel force, which is growing in size and claiming responsibility for a rising number of attacks against the Syrian army and intelligence services, lacks weapons and ammunition.
"If we had what we need, we could finish off the regime in 10 days," said Khaled, a sniper with the FSA's Tel Kalakh Martyrs' Brigade. "Every time we fire a shot, we have to think carefully about where that bullet is going."
The insurgency campaign mounted by the FSA, which includes assassinations, roadside bomb attacks, ambushes and crowd protection, is reshaping the 11-month struggle. What began as protests against the regime has turned into an armed struggle in which more than 6000 people have died and which has brought the country to the brink of a sectarian civil war.
Critics point to the logistical difficulties of supplying weapons to the FSA and the lack of clarity over the composition of the rebel force. A declaration of support for the uprising by Ayman al-Zawahiri, the leader of al-Qa'ida, has triggered alarm that the struggle may attract jihadist militants.
Small quantities of individual weapons are smuggled from Lebanon. Larger amounts are crossing from Iraq into the hands of Sunni tribes and Kurdish groups in eastern Syria, according to Western intelligence sources. The weapons are being stockpiled in the east because of difficulties in transporting them undetected across hundreds of kilometres of desert to the protest hubs in the western half of the country.
The Turkish border is regarded as the most favourable transit point for smuggled arms. Turkey has come out strongly against the Assad regime and hosts the leadership of the FSA. Furthermore, much of Syria's northern Idlib province is under the control of rebel groups, according to opposition activists and FSA fighters.
The 300 to 400 fighters of the Tel Kalakh Martyrs' Brigade are based in the eponymous town, 3km north of the Lebanese border near Homs. The brigade is split into combat units of between six and 10 fighters, each equipped with a rocket-propelled grenade launcher and a light machine gun, alongside individual weapons. Khaled, a former soldier in an air defence regiment who deserted in October, said one of the main sources of weapons for the FSA was the Syrian army.
"We have some senior officers who are with us either because they believe in our cause or because we can bribe them. They are our only way of getting more advanced weapons, such as Kornets," he said, referring to the Russian anti-tank missile.
Hezbollah used Kornet missiles to deadly effect against Israel's top Merkava tanks in Lebanon during the 2006 war.
The Syrian army has begun deploying its more heavily armoured T-80 tanks.
A video recently posted on YouTube shows a burning T-72 tank said to have been destroyed by the FSA in Zabadani. The clip shows what appears to be a Kornet or the shorter-range Metis anti-tank missile, one of 60 the FSA claimed it had seized from a captured military depot.