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:

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?

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.