The Hayat Tahrir al-Sham (HTS) rebel group and allied factions launched a major offensive on Syrian military positions in the western countryside of Aleppo province, resulting in territorial gains and 89 deaths, according to a war monitor.

The Syrian Observatory for Human Rights reported that the HTS and factions from the al-Fatah al-Mubin operations room seized control of 21 villages, towns, and strategic sites in less than 12 hours since the start of the operation, dubbed “Deterring Aggression,” Xinhua news agency reported.

It noted that 89 combatants died in Wednesday’s clashes, including 52 fighters from the HTS and its supporting factions and 37 soldiers from the Syrian government forces.

Additionally, five Syrian soldiers were captured by the HTS, which has also seized weapons depots, armored vehicles, and heavy weapons, it said.

In response to the offensive, Russian warplanes conducted airstrikes using vacuum missiles on the rear positions of the factions around the city of Atarib, and Syrian government forces shelled Atarib, Darat Izza, and surrounding villages with hundreds of artillery shells and rockets, the observatory reported, adding that Syrian and Russian warplanes carried out 26 airstrikes during the clashes.

A day earlier, the military buildup of the HTS prompted significant displacement of civilians from Atarib and nearby villages in the western Aleppo countryside, according to the observatory.

The HTS, formerly the Nusra Front, is considered a terrorist organization by Syria, Russia, and several other countries.