The Syrian rebel group Hayat Tahrir al-Sham (HTS), which seized the city of Aleppo in a shock offensive over the weekend, is an Islamist movement that has long ruled swaths of the country's northwest.

The group has sought to moderate its image in recent years, including by cutting ties with its one-time sponsor al-Qaida, but it faces an uphill battle convincing Western governments it has fully renounced hard-line jihadism, experts say.

Aleppo had been held by Syrian government forces since late 2016.