Rebel groups attacked pro-Syrian government forces west of Aleppo with three car bombs on Saturday, rebel and Syrian military sources said to Reuters, in an intensification of fighting in the northwest following Syrian government gains this week.
Two of the attacks were carried out by suicide bombers with the militant group Hayat Tahrir al-Sham while a third car bomb was set off by remote control, a Hayat Tahrir al-Sham source said.
A news outlet linked to the group, Ebaa, published a video which it said showed elite Tahrir al-Sham fighters pledging "allegiance to death and jihad" before the attack on Jamiyat al-Zahraa, watched by the group's leader, Abu Mohammad al-Jolani.
The Hayat Tahrir al-Sham source said the attacks had targeted the "Iranian occupation militias", a reference to Iran-backed groups fighting in support of Assad.
Syrian state news agency SANA said army troops had destroyed four car bombs before they reached their targets. Syrian army forces were firing rockets and artillery at militant groups on the Jamiyat al-Zahraa front, it said. Militants had also fired rockets at residential districts of Aleppo.
The two sides gave conflicting accounts of the outcome of the attack.
A news outlet run by Lebanon's Hezbollah, which fights in support of Assad, said the Syrian army had thwarted a "fierce attack" by the Nusra Front, as Jolani's group was known until it broke ties with al Qaeda in 2016.
Last week, reports suggested that 40 regime soldiers were killed in an offensive by opposition groups in Idlib.
Since April last year, the regime has led a campaign of constant aerial bombardment of the province with Russian support, aiming to recapture the last major opposition stronghold in the country in its nine-year-long civil war. This campaign was launched despite the deal between Turkey and Russia in September 2018 to make Idlib a de-escalation zone in which civilians could live safe from the conflict.
Last week, the Syrian regime reportedly captured ten towns and villages in less than 48 hours, in the embattled province of Idlib in the north-west of the country, marking its most rapid advance in its campaign to recapture the last major opposition stronghold.
Estimates say that at least 700,000 people have been displaced by the regimes campaign. Turkey, which fears a fresh wave of migrants piling into its territory, adding to the more than 3.6 million Syrians already there, said on Friday it would not tolerate new threats near its border and would act militarily if needed.