Assault on Aleppo: who are the Syrian rebels HTS and why are they advancing?

The fast-moving offensive began on Wednesday, surprising forces loyal to Bashar al-Assad and his allies

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Eight years ago, indiscriminate Russian airstrikes helped the forces of the Syrian president, Bashar al-Assad, drive rebels from Aleppo - a crucial turning point in the country's civil war, which has largely been in a state of stalemate since 2020.

Over the weekend a stunning rebel offensive seized Aleppo again - and the Assad regime now faces its greatest threat in years. Here's what you need to know.