The rapid advance on Aleppo came just four days into a surprise rebel offensive that is the most intense escalation in years in a civil war that was mostly dormant.

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,

Russia launched air raids in parts of the city overnight "for the first time since 2016", a monitoring group said.