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.

Syrian armed opposition forces have entered Aleppo just three days into their surprise offensive, marking the first time they have set foot in the country’s second largest city since government forces recaptured the city in 2016.

Thousands of Syrian opposition fighters, led by the Hayat Tahrir al-Sham (HTS) group, have pushed forward with their offensive in the northwest, moving closer to the city of Aleppo and capturing several key towns and villages in the region,