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.

Cities in Syria have been hit by Russian air strikes throughout the weekend, as anti-government rebels have advanced in Aleppo. Hundreds of people have been killed in fighting since Wednesday, when the current offensive began. Here are some key takeaways from our reporting over the past few hours:

Sham, a powerful Syrian rebel faction, has launched offensive in Aleppo by taking military bases and villages from Assad's forces. This marks a significant escalation of the civil war in Syria, with HTS posing a major threat to Assad's regime.