Syria's second and largest city Aleppo has become a key battleground in the 17-month uprising against Bashar al-Assad's government. Aleppo city is the country's commercial capital and its biggest urban area, near the border with Turkey where rebels have taken control of a number of border crossings. The Free Syrian Army (FSA) launched a major offensive in Aleppo a week ago but the army is launching a major push to drive out rebels fighters, taking two days to manouever heavy weapons into positions around the city.