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.

The surprise attack, led by the Islamist group Hayat Tahrir al-Sham, was the boldest rebel assault for years in the civil war that has been frozen.