Among the worst incidents last month was as a mortar bomb attack on Damascus University that left 15 students dead. The group's unofficial estimate of the total number killed since Syria's confliect erupted two years ago is around 120,000. The UN puts the estimated figure at some 70,000. Aleppo has seen some of the fiercest fighting. It is a stronghold of President Bashar al-Assad's forces and viewed as a prize by insurgents. President Assad labels them terrorists and claims they are funded by Gulf and other foreign powers. The Syrian Observatory believes most of the 2,250 opposition fighters killed came from abroad.