Syrian government forces killed 22 rebels overnight near Idlib province, in the deadliest such attack in an area where a recent truce is to be enforced, a monitor said Friday.
Fighting erupted when government troops seized a position in a rural area in the north of neighbouring Hama province that had been held by the Jaish al-Izza group, the Syrian Observatory for Human Rights said.
Idlib and some surrounding areas are the last major rebel bastion in Syria, where the Russian-backed government has in recent months retaken much of the territory it had lost since the civil war erupted in 2011.
It had threatened an assault on rebel territory, home to around three million people, but a deal for a de-militarised buffer zone around it was reached in September between Moscow and rebel backer Ankara.
Several deadly skirmishes have occurred since the deal but 22 is the highest number of known fatalities in a single incident inside the planned buffer zone, the Observatory said.
"This is the highest death toll in the de-militarised zone since it was announced," Rami Abdel Rahman, head of the Britain-based monitoring group, told AFP.