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,

The rebels have made stunning gains against President Bashar al-Assad’s forces, with Russia, Iran and Hezbollah distracted by other conflicts.

Syria's civil war has exploded back into life after Islamist rebels launched a lightning offensive on the northern city of Aleppo.