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

Syria's civil war has taken a dramatic turn, with dictator Bashar Assad once again leaning on Russian support after a shock offensive by Islamist rebels in Aleppo.

Syrian rebels have swept through parts of the country at lightning pace, taking control of the the second-largest city, Aleppo. But who are they and what are their aims?