Syrian opposition forces have seized most of Aleppo after launching a surprise offensive in recent days that ousted government forces from the country’s second-largest city. The offensive is being led by an armed group called Hayat Tahrir al-Sham, a former al-Qaeda affiliate that cut ties with them in 2017. Syrian and Russian forces have retaliated with airstrikes on rebel-held areas, with the London-based Syrian Observatory for Human Rights reporting 446 deaths in Syria since Wednesday. The rebel advance into Aleppo is the most significant turn in the Syrian civil war since 2020, when rebel forces were forced to retreat to Idlib. The offensive was launched at a time when the key backers of Bashar al-Assad’s government — Russia, Iran and Hezbollah — are also focused on other conflicts. “It was a surprise offensive that people did not expect at all,” says Associated Press reporter Kareem Chehayeb.