The Russian and Syrian air forces bombed rebel-held northwest Syria near the border with Turkey on Thursday to push back a rebel offensive that captured territory for the first time in years, Syrian army and rebel sources said.
Rebels led by militant group Hayat Tahrir al Sham on Wednesday launched an incursion into a dozen towns and villages in northwest Aleppo province controlled by Syrian President Bashar al Assad.
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 "terrorists" who had launched a "large attack on a wide front."
The army said it was cooperating with Russia and unnamed "friendly forces" to regain ground and restore the situation to what it was.
Rebels advanced almost 10 km (6 miles) from the outskirts of Aleppo city and a few kilometres away from Nubl and Zahra, two Shi'ite 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.
Rebels say the campaign was in response to stepped-up strikes in recent weeks against civilians by the Russian and Syrian air forces on areas in southern Idlib, and to preempt any attacks by the Syrian army, which they said was building up troops near front lines with rebels.
They say over 80 people, mostly civilians, have been killed since the start of the year in drone strikes on rebel-held villages.
Damascus says it is waging a war against al Qaeda-inspired militants and denies targeting civilians indiscriminately.
Rebels say Damascus is taking advantage of wider conflict in the region to try to seize control of Syria's last major rebel-held territory near the border with Turkey, where over three million people live.
Reporting by Suleiman Al-Khalidi