Syrian rebel fighters began preparations to seize Aleppo a year ago but the operation was delayed by war in Gaza and ultimately launched last week when a ceasefire took hold in Lebanon, the head of Syria's main opposition abroad told Reuters.

Syrian and Russian jets are stepping up strikes on opposition forces in northern Syria in retaliation for the sudden offensive that has cost the regime control of the country’s second largest city, Aleppo.

Rebels captured Syria's second-largest city, Aleppo, over the weekend and advanced toward Hama in a surprise incursion that reignited Syria's 13-year-old civil war and embarrassed President Bashar al-Assad's forces.