Beirut - Extremists on Thursday killed four pro-regime fighters in Idlib province, the rebel stronghold where Russia and Turkey have agreed to set up a buffer zone, a monitor said.
The northwestern province is the last major area still outside regime control, after a string of ferocious assaults this year put most of the country back in regime hands.
Regime ally Russia and rebel backer Turkey agreed to establish the buffer zone in September.
It was due to come into force in mid-October but some clauses of the plan have been delayed, as repeated clashes erupted between extremists, rebels and government forces.
At dawn on Thursday, extremists from Hayat Tahrir Al Sham, a faction led by former Al Qaida fighters, attacked a government position in the east of the province, said the Britain based Syrian Observatory for Human Rights.
“Four regime fighters were killed in the assault, and a member of HTS also died,” said Observatory director Rami Abdul Rahman.
“There is an ongoing exchange of artillery fire between the two parties” in land that is part of the planned demilitarised zone, he added.
The agreement between Russia and Turkey to create the buffer zone was aimed at staving off a government military assault on the province.
As set out under the deal, rebel groups announced they had withdrawn heavy artillery from the zone, but extremists including HTS refused to leave the area.
Artillery fire by regime forces killed at least seven civilians in Idlib on Friday last week, the Observatory said.
Syria’s Foreign Minister Walid Mua’llem expressed dissatisfaction this week with the implementation of the agreement, and criticised Turkey for shortcomings.