The United States on Saturday said Syrian leader Bashar al-Assad lost control of Aleppo because of his reliance on Russia and Iran.

Syria’s “reliance on Russia and Iran,” along with its refusal to move forward with a 2015 peace process outlined by the UN Security Council, “created the conditions now unfolding,” National Security Council spokesman Sean Savett said in a statement.

He added: “At the same time, the United States has nothing to do with this offensive, which is led by Hayat Tahrir al-Sham (HTS), a designated terrorist organization.”

The Syrian army said on Saturday dozens of its soldiers had been killed in a major attack led by Islamist Hayat Tahrir al-Sham rebels who swept into the city of Aleppo, forcing the army to redeploy in the biggest challenge to President Bashar al-Assad in years.

In his first public comments since the start of the offensive, released by the state news agency Saturday evening, Assad said Syria will continue to “defend its stability and territorial integrity against terrorists and their supporters.” He added that Syria is able to defeat them no matter how much their attacks intensify.

Russia’s Defence Ministry said its air force had carried out strikes on Syrian rebels in support of the country’s army, Russian news agencies reported. The strikes followed what was the boldest rebel assault for years in a civil war where front lines had largely been frozen since 2020.

Hayat Tahrir al-Sham, or HTS, once known as the Nusra Front, is designated a terrorist group by the U.S., Russia, Turkey and other states. Assad is a close Moscow ally.

Aleppo had been firmly held by the government since a 2016 victory there, one of the war’s major turning points, when Russian-backed Syrian forces besieged and laid waste to rebel-held eastern areas of what had been the country’s largest city.

Acknowledging the rebel advance, the Syrian army command said insurgents had entered much of Aleppo.

After the army said it was preparing a counterattack, airstrikes targeted rebel gatherings and convoys in the city, the pro-Damascus newspaper al-Watan reported. One strike caused casualties in Aleppo’s Basel square, a resident told Reuters.

The state-run Russian Centre for the Reconciliation of the Enemy Parties in Syria said missile and bomb strikes against the rebels had targeted “militant concentrations, command posts, depots, and artillery positions” in Aleppo and Idlib provinces. It claimed about 300 rebel fighters had been killed.

Images filmed on Saturday showed people posing for photos on a toppled statue of Bassil al-Assad, late brother of the president. Fighters zipped around the city in trucks and milled around in the streets. A man waved a Syrian opposition flag as he stood near Aleppo’s historic citadel.

The Syrian military command said militants 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.

Two rebel sources also said the insurgents had captured the city of Maraat al Numan in Idlib province, bringing all of that area under their control.

The fighting revives the long-simmering Syrian conflict as the wider region is roiled by wars in Gaza and Lebanon, where a truce between Israel and the Iran-backed Lebanese group Hezbollah took effect on Wednesday.

With Assad backed by Russia and Iran, and Turkey supporting some of the rebels in the northwest where it maintains troops, the offensive has brought into focus the conflict’s knotted geopolitics. Fighting in the northwest had largely abated since Turkey and Russia reached a de-escalation agreement in 2020.