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?

Forces opposed to President Bashar al-Assad have captured the Aleppo airport and are attacking the western city of Hama, according to local officials and a Britain-based war monitor.

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.