Regime air strikes Monday killed 10 civilians in Syria's last major opposition bastion, where deadly clashes between regime forces and armed groups have escalated in the past two days, a monitor said.
The raids also wounded 15 civilians in a market in the town of Maaret al-Numan in the jihadist-run province of Idlib, the Britain-based Syrian Observatory for Human Rights added.
That came as regime forces and armed groups were locked in heavy clashes on the southeastern edge of the region, with almost 100 fighters killed in two days, the Britain-based monitor said.
The battles on the edge of Idlib since Saturday are the most deadly since a Russia-brokered ceasefire went into effect in late August, it said.
"Fighting raged at dawn Monday on several axes in the southeastern Idlib countryside," the monitoring group said.
Fifty-one regime fighters had been killed over 48 hours, while 45 of their opponents including 31 jihadists had also lost their lives, the Observatory said.
The Syrian government does not usually divulge casualty figures.
The Idlib region, home to around three million people including many displaced by Syria's eight-year civil war, is largely under the control of a group dominated by a former Al-Qaeda affiliate.
It is one of the last holdouts of opposition to forces backing Syrian President Bashar al-Assad.
The president has long maintained that his government will eventually reimpose its control over the northwestern region on the border with Turkey.
The late August ceasefire came months into a devastating Russia-backed regime offensive that killed around 1,000 civilians and ousted hundreds of thousands from their homes.
But sporadic clashes and deadly Russian and regime bombardment on the jihadist-held bastion have however persisted, with 160 civilians including 45 children killed during that time.
The war in Syria has killed more than 370,000 people and displaced millions since it erupted in 2011 with the brutal repression of anti-government protests.