Syrian rebels opposed to President Bashar al-Assad have returned to Aleppo after nearly a decade, prompting the closure of the city's airport and roads. The rebels, led by the Islamist militant group Hayat Tahrir al-Sham, have made a surprise sweep through government-held towns and reached the heart of Aleppo. Russia, a key ally of Assad, has promised additional military aid to Damascus to counter the rebels. The Syrian army has been ordered to withdraw from the areas of the city that the rebels have entered. The attack is the largest since a de-escalation deal was reached between Russia and Turkey in March 2020.