Syria Under Siege

We turn to an epic battle over the country's industrial power center, the city of aleppo. Rebel sources made big strides. Abc's alex marquardt has the details. Reporter: A syrian newspaper warned it... See More

We turn to an epic battle over the country's industrial power center, the city of aleppo. Rebel sources made big strides. Abc's alex marquardt has the details. Reporter: A syrian newspaper warned it will be the mother of all battle. A showdown has been looming for days. Opposition and assad forces massing around aleppo, syria's commercial capital. Regime vowing to snuff out opposition fighters who captured territory. The bbc's ian pannell has been there. It's been an incredibly hot day in more ways than one. There's been constant activity. The sound of bangs through the air explosions. Not far from here. Reporter: Regime forces pounded the city with tanks and helicopter gunships. Unverified video from today showed a fighter jet. The jet was used for the first time in battle this past week. The violence has sent residents fleeing their homes in droves. The united states has warned of potential blood bath. This is the concern that we will see a massacre in aleppo and that's what the regime appears to be lining up for. The fighting in aleppo follows unprecedented clashes in the capital damascus. The rebels are clearly gaining in confidence but still hugely outmatched in terms of fire power. They know bringing the fight to syria's biggest farina ecities, and capturing them would deal a deadly blow to the assad regime.