Meantime, Western powers are reported to be moving military equipment to the more secular Free Syrian Army through Jordan, Syria's highly vulnerable southern neighbor.
The Islamist forces, which have made major gains in northern Syria, are largely armed by Saudi Arabia and Qatar through Turkey, Syria's northern neighbor.
These events give weight to concerns of a looming showdown in Syria between the rebel rivals that will in all likelihood intensify the tensions already gripping a volatile region torn by political upheaval, insurgencies and sectarian schisms that transcend national boundaries.
The fear is that the growing gulf between the two coalitions in Syria, one Islamist and calling for an Islamic state, the other secular and oriented toward democracy, could lead to a new conflict once the regime of President Bashar Assad is brought down by his overwhelmingly Sunni enemies.
And most observers say that's just a matter of time.
To make matters worse, Iraq, Syria's eastern neighbor, is also in turmoil with al-Qaida's Sunni suicide bombers waging a murderous campaign against the Shiite-dominated government of Prime Minister Nouri al-Maliki.
"A major blow-out is coming in the second half of 2013 when Sunni jubilation at the collapse of the Assad regime in Syria may collide head-on with the Maliki government's paranoia about being the next domino to fall," warned analyst Michael Knights of the Washington Institute for Near East Policy.
There have been growing signs that hardliners within the two rebel movements are squaring off.
In January, Thaer al-Waqqas, leader of the FSA's al-Farouq Brigade was killed in northern Syria amid suspicions he was involved in the death of Firas al-Absi of the jihadist al-Nusra Front.
The two groups have engaged in open warfare in recent weeks.
On Sunday, Mohammed al-Daher, a popular al-Farouq commander in eastern Syria, was badly wounded in an apparent attempt to assassinate him by the al-Nusra Front.
Military analysts say it could take weeks before the rebels are ready to unleash a major offensive aimed at Damascus, where rebel forces hold several positions on the capital's outskirts.
Their main requirements in terms of weaponry are anti-tank and anti-aircraft missiles to counter the regime's armor and air power.
But it's clear that finally the Americans and their European allies are being pushed into supplying the rebels with weapons even though they've tried assiduously over the months not to get become directly involved in a civil war that threatens to destabilize the entire Levant.
It could trigger a regional sectarian war, with the centuries-old religious schism that has fractured Islam since the death of the Prophet Mohammed in the eighth century at its core, with Sunni Saudi Arabia and Shiite Iran the main protagonists.
"As fighting in Syria presses on, the various groups that propagate the conflict, ever more confident that they will bring about the fall of ... Assad, eventually will succumb to political and ideological rivalries," cautioned the U.S. global security consultancy Stratfor.
It argues the rebels will no doubt seek to avoid serious clashes, if only because Assad, although increasingly seen as on the defensive these days, retains sizeable and coherent forces, aided by Iran and Russia.
The divisions in the rebel ranks, of course, go beyond the FSA and the al-Nusra Front.
There are myriad differences between other groups, each with their own agenda and vision of what should happen after Assad's hated Alawite minority regime is no more.
But for now, al-Nusra's growing emphasis on establishing an Islamic state once Assad's gone can only deepen those differences.
That, in the short term, could make it extremely difficult to organize the joint offensive that will be needed to seize Damascus, the seat of Alawite power.
In the meantime, al-Nusra, which Western intelligence officials say is emerging as an entirely separate force from al-Qaida in Iraq which fostered it, is growing in strength by the day as diehard Islamists from around the world, many veterans of other wars, flock to its banner.