ALEPPO -- Syria's biggest city is in danger of becoming a slaughterhouse. President Bashar al-Assad's army -- backed by Iran and Russia -- had previously surrounded Aleppo, but was not able to lock it down.

A key turning point was reached over the weekend when a newly formed coalition of opposition fighters, including some recently affiliated to al Qaeda, managed to break through government lines.

Drone footage released by Syrian rebels shows the moment a suicide bomber blew himself up, allowing rebels to break through government front lines. CBS News

They released drone footage which shows the moment a suicide bomber drove a truck through the city and blew himself up, allowing rebel groups to advance forward and seize a military complex with small arms, ammunition and heavy artillery.

It all looked so different just two weeks ago. After years of stalemate in the fight for control of the city, government troops backed by Russian airstrikes seized the rebel's last remaining supply route and cut off an estimated 250,000 civilians.

In a desperate bid to break the siege, opposition forces launched a successful counter offensive. They surprisingly were able to take over the main road into the government-held part of the city where an estimated 1.2 million people live.

The gains by the opposition were greeted with celebrations in the rebel-controlled parts of Aleppo. But they could be short-lived.

There are growing fears of food and fuel shortages. And the Syrian military, backed by its allies, says it is amassing thousands more fighters along the front lines.

The fight for Aleppo is clearly intensifying and could to become a pivotal battle in this war, but as this stage it's unclear if either side can actually win.