BEIRUT (Reuters) - Shelling in Syria’s Idlib province killed at least seven civilians on Friday, the largest one-day loss of life there since Russian air strikes stopped in mid-August, a war monitor said.

Idlib province is part of the Syrian opposition’s last big foothold in the country and is effectively a zone of Turkish influence under de-escalation agreements reached between opposition-backer Turkey and Damascus-ally Russia.

A Russia-Turkey deal in mid-September also created a demilitarized zone on the region’s frontline with Syrian government forces, from which rebel groups had to withdraw heavy weaponry.

The Syrian Observatory for Human Rights has reported regular exchanges of shelling since then in south-east Idlib province and the western outskirts of Aleppo city which have caused a few deaths in both rebel- and opposition-held sides of the frontline, but Friday marked an escalation.

The war monitor said seven people, including three women and three children, died in Rafa village in southeast Idlib province on Friday. Shelling by Syrian government forces also hit other areas nearby, the Observatory said.

The U.N. says around 3 million people live in rebel-held Idlib and adjacent areas and has warned that a battle to restore Syrian President Bashar al-Assad’s control over the zone could be the worst of the seven-year-old war.