Bombardment killed 13 civilians in northwest Syria on Sunday, the large majority in regime fire on areas of the jihadist-held Idlib region, a war monitor said.
The violence was the latest to threaten a seven-month-old truce intended to stave off a regime offensive on the region held by Syria's former Al-Qaeda affiliate.
Sunday's shelling and rocket fire by regime forces killed nine civilians in several areas of Idlib, the Syrian Observatory for Human Rights said.
They included five people in the town of Nayrab, three in Saraqeb, and one in the village of Al-Khuwayn, the Britain-based monitoring group said.
The Observatory said bombardment by Islamist fighters on the regime-held town of Masyaf in the adjacent province of Hama killed four civilians.
The rocket fire hit a hospital killing members of its staff, state news agency SANA said.
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Regime ally Russia and rebel backer Turkey in September inked a buffer zone deal to prevent a massive regime offensive on the Idlib region, near the Turkish border.
But the region of some three million people has come under increasing bombardment since former Al-Qaeda affiliate Hayat Tahrir al-Sham overran the region in January.
More than 30 civilians have been killed in regime bombardment on Idlib since Wednesday alone, according to the Observatory.
Syrian Foreign Minister Walid Muallem this week said his government was growing impatient to recapture Idlib, the last region outside its control apart from the Kurdish-held northeast where the United States retains a troop presence.
The UN humanitarian office OCHA has said the escalating violence had already killed 90 civilians in the Idlib region in March, nearly half of them children.
The escalation pushed more than 86,500 people to flee their homes in February and March, it added.
At least 370,000 people have died in Syria since the civil war erupted in 2011 with the brutal repression of anti-government protests.