Beirut: Extremists on Friday killed 22 regime fighters near a planned buffer zone around Syria’s last major rebel bastion of Idlib, a monitor said.

A September deal between regime ally Russia and opposition backer Turkey aimed to set up a demilitarised zone around the northwestern region to protect it from a regime assault.

But its implementation has been stalled since extremists who hold around 70 per cent of the planned buffer zone failed to withdraw by mid-October, and intermittent clashes have since rocked the area.

Early Friday, extremist groups attacked regime forces in the northwest of Hama province near the planned zone, the Britain-based Syrian Observatory for Human Rights said.

Twenty-two regime fighters were killed in the attack, Observatory head Rami Abdul Rahman said, explaining a previous death toll of nine increased after the bodies of missing fighters were found.

The attackers included the Al Qaida-linked Hurras Al Deen group, which has publicly rejected the Russian-Turkish deal, he said.

The monitor said it was the highest regime death toll from the sporadic clashes around the proposed zone since the deal was agreed.

State news agency SANA reported a military source as saying that “a terrorist group tried to infiltrate one of our advanced position near Sarmaniya” in Hama, killing and wounding regime fighters, without giving a death toll.

The lion’s share of Idlib is held by Hayat Tahrir Al Sham (HTS), an alliance led by Al Qaida’s former Syrian affiliate.

Under the September 17 deal, all fighters in the zone were supposed to withdraw their heavy weapons and extremists including HTS and Hurras Al Deen were supposed to leave.

On Thursday, Russian spokeswoman Maria Zakharova criticised “sporadic clashes”, as well as “provocations” by HTS in northwestern Syria.

Late last month, Syria’s Foreign Minister Walid Muallem expressed dissatisfaction with the implementation of the Idlib deal, and criticised Turkey for the shortcomings.

He said heavy weapons had not been withdrawn and accused Ankara of not wanting to “respect its obligations”.

Syria’s war has killed more than 400,000 people since it erupted in 2011 with the brutal repression of anti-regime protests.