Syrian opposition forces have taken control of much of the country’s second largest city Aleppo, according to video verified by CNN and residents in the city. A rebel alliance launched a surprise attack this week,

The Syrian military said on Saturday that rebels had entered large parts of Aleppo city during an offensive in which dozens of soldiers had been killed, forcing the army to redeploy - the biggest challenge to President Bashar al-Assad in years.

Opposition fighters have seized control of most parts of Aleppo, Syria's second largest city, after launching a massive surprise offensive against the government forces, a war monitor reported on Saturday.