The first new heavy weapons are being used on Syria's front lines following President Barack Obama's decision to put Western military might behind the official opposition.
Rebel sources said Russian-made "Konkurs" anti-tank missiles, supplied by America's key Gulf ally, Saudi Arabia, have been put to destructive effect and may have held up a promised regime assault on Aleppo.
A handful of the missiles were previously already in use and in high demand after opposition forces looted them from captured regime bases.
More have now arrived, confirming reports that the White House has lifted an unofficial embargo on its Gulf allies sending heavy weapons to the rebels.
Last week, the White House said it would send military support to Syria's opposition after concluding that President Bashar al-Assad's regime had used chemical agents against them.
Unlike rocket-propelled grenades, the Konkurs - Contest in English - can penetrate the regime's most advanced tanks, Russian-made T72s.
"We now have supplies from Saudi Arabia," a rebel sources aid. "We have been told more weapons are on their way, even higher-end missiles."
At the G8 this week Vladimir Putin, the Russian President, condemned the West's attempts to send arms to the opposition.
On Syria's front lines, rebels are already using Russian missiles to destroy the regime's Russian tanks. Thanks to Russian backing over the last half century, Syria's army was the best equipped in the region, and its captured bases have handed a limited number of anti-tank and anti-aircraft missiles to the opposition. But the number of Konkurs missiles seen in videos escalated at the beginning of this month, tangible evidence of the new Saudi supply line.
In the hills above the Syrian village of Kafra Hamra, north of Aleppo, rebels talked almost lovingly of the Konkurs as they kept watch on the regime's tanks 800m away. "We have one or two left but my unit has run out already," said Abdullah Da'ass, a burly, bearded fighter with the Free Men of Syria brigade. "We were given five. We fired four, and took out four regime tanks, and one was a dud."
Assad's regime has hundreds of T72s in northern Syria. The future of this war may depend on how many more portable missile systems the rebels are given. In the past two weeks the tanks have made a number of sallies, testing rebel lines, but have been driven back, rebels say.
After the fall of Qusair on June 5, the regime promised an all-out attack on Aleppo, but it has not yet materialised. Ahmed Hafash, the leader of Free Men of Syria, the non-Islamist brigade leading the defence of Kafra Hamra, said he expected the assault to drive north away from the city. Five kilometres northeast lie two loyalist Shia towns, Nobbul and Zahra, where a regime general has raised a local militia several thousand-strong and flown in reinforcements from the Lebanese militia Hizbollah.
The regime has 20,000 men based around the Air Force Intelligence barracks behind the front, the rebels say, but has spared 2500 for this front.
The rebels have possibly a similar number, but whether the tanks rolling over the hills can punch through them depends on their defences.