Syrian Violence Continues As Civilians Caught In 'Crossfire’ Battle For Aleppo (Video)

This amateur video appeared on a social media website showing artillery pounding Syria's biggest city Aleppo.

But as the shells rain down, rebel fighters say troops loyal to Syrian President Bashar al-Assad have been forced to retreat.The fight for Syria's second city -- dubbed the "mother of all battles" by government authorities -- has quickly added to the country's already staggering death toll.But a spokesperson for the United Nations Supervision Mission in Syria said the greatest concern is the safety of civilians.

The battle for Aleppo has become a crucial test for both sides in the 17-month-old conflict.Neither Assad's forces nor the Free Syrian Army can afford to lose if they hope to prevail in the wider struggle for control of Syria.

The United Nations says that an estimated 200,000 people have fled the fighting in past two days. The UK-based Syrian Observatory for Human Rights reported 135 deaths on Wednesday while the Local Coordination Committees gave a figure of 170. Activists estimate some 20,000 people have died since March last year.