At least 44 people have been killed and dozens hurt in Syrian government air strikes on markets in two rebel-held towns in Idlib province, activists say.
The Syrian Observatory for Human Rights said 37 died in Maarat al-Numan and another seven in nearby Kafranbel.
The death toll was expected to rise as many of the injured were in a serious condition, the monitoring group added.
Escalating violence in the north-west in recent days has left a seven-week truce on the verge of collapse.
Earlier, the head of the main Syrian opposition umbrella group said it had suspended formal participation in UN-led peace talks in Geneva in protest at alleged government violations.
Riad Hijab declared that the High Negotiations Committee could not take part while people were dying. The process, he said, was only increasing their suffering.
On Monday, 10 rebel groups announced they had begun a new “battle” in response to what they said was a surge in attacks on residential areas and displaced people.