Russian and Syrian warplanes bombed rebel-held northwest Syria near the border with Turkey on Thursday to push back an offensive that captured territory for the first time in years, Syrian army and rebel sources said.
Rebels led by Hayat Tahrir al-Sham (HTS) launched an incursion on Wednesday into a dozen towns and villages in the northwestern province of Aleppo, which is controlled by Syrian President Bashar al-Assad's forces.
The attack was the biggest since March 2020 when Russia, which backs Assad, and Turkey, which supports the rebels, agreed to a ceasefire that ended years of fighting that uprooted millions of Syrians opposed to Assad's rule.
In its first statement since the surprise campaign, the Syrian army said it had inflicted heavy losses on what it described as terrorists who had attacked on a wide front.
A Syria war monitor on November 28, said clashes between the army and HTS killed more than 130 combatants in the worst fighting in the country's northwest in years.
The army said it was cooperating with Russia and unnamed "friendly forces" to regain ground and restore the situation.
Rebels advanced almost 10 km (6 miles) from the outskirts of Aleppo city and a few kilometres away from Nubl and Zahra, two Shia towns where Lebanon's Iran-backed Hezbollah has a strong militia presence, an army source said.
They attacked al-Nayrab airport east of Aleppo, where pro-Iranian militias have outposts.
Russian jets pounded newly captured areas and hit populated towns in the last opposition-held enclave, according to two army sources.
The opposition-run rescue service known as the White Helmets said at least 16 civilians were killed in the rebel-held town of Atareb when a Russian jet bombed a residential area.
The main Aleppo-Damascus highway was closed as a result of the fighting, residents and witnesses said.
Rebels say the campaign responded to stepped-up strikes in recent weeks against civilians by the Russian and Syrian air forces on areas in southern Idlib province, in Syria's far northwest, and to preempt any attacks by the Syrian army, which they said was building up troops near front lines with rebels.
Meanwhile Iranian state media said Revolutionary Guards Brigadier General Kioumars Pourhashemi, a senior Iranian military adviser in Syria, was killed in Aleppo by rebels.
Iran has sent thousands of fighters to Syria during the Syrian war. While these have included members of the Guards, officially serving as advisers, the bulk have been Shi'ite Muslim militiamen from all over the region.
Pro-Iranian militias have an extensive military presence in the Aleppo countryside.
Turkish security sources said on Thursday the rebels initially launched a limited operation after attacks by Syrian government forces, and expanded the operation after government forces abandoned their positions.
The Turkish sources said the rebel movements remained within the boundaries of a de-escalation zone in Idlib, which was agreed in 2019 by Russia, Iran and Turkey with the aim of reducing hostilities between the rebels and government forces.