Fighters from the Hay’et Tahrir al-Sham armed group have swept into the city of Aleppo after a lightning offensive, forcing the Syrian army to withdraw from the northern city after eight years.

The rebel assault is the most intense fighting seen in northwestern Syria since 2020, when Russia and Turkiye agreed to a deal to de-escalate the conflict after government forces seized areas previously controlled by opposition fighters.

The government forces have been in control of Aleppo since 2016, nearly a year after Russia intervened in support of President Bashar al-Assad.

Russia’s Ministry of Defence said its air force carried out strikes on Sunday in support of the country’s army, Russian news agencies reported.

Hay’et Tahrir al-Sham, earlier known as al-Nusra Front, is designated a terrorist group by the United States, Russia, Turkiye and some other states.

In Washington, the White House National Security Council said it was closely monitoring the situation and had been in contact with regional capitals over the last 48 hours.

Peaceful protests erupted against al-Assad following the 2011 Arab Spring protests. But soon the protests descended into violence and later turned into a proxy war after a widespread crackdown on opposition figures and protesters.

Hundreds of thousands of people have been killed and millions displaced since 2011. Most major fighting halted years ago after Iran and Russia helped al-Assad’s government win control of most land and all main cities. Rebels were pushed to the Idlib province bordering Turkiye.

After the army said it was preparing a counterattack, air raids targeted rebel gatherings and convoys in the city, the pro-Damascus newspaper Al-Watan reported.

The Syrian military command said rebels had attacked in large numbers and from multiple directions, prompting “our armed forces to carry out a redeployment operation aimed at strengthening the defence lines in order to absorb the attack, preserve the lives of civilians and soldiers”.

The rebels also took control of Aleppo airport, according to a statement by their operations room and a security source.

The fighting revives the long-simmering Syrian conflict as the wider region is roiled by wars in Israel’s war on Gaza and Lebanon. A ceasefire between Israel and Hezbollah took effect on Wednesday.