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, according to BBC News.

The Syrian Observatory for Human Rights said 37 died in Maarat al-Numan and another seven in nearby Kafranbel.

The monitoring group added that three children were among the victims and the death toll was expected to rise.

Escalating violence in the country in recent days has left a seven-week partial truce on the verge of collapse.

Earlier, the head of the main Syrian opposition umbrella group said it had suspended its formal participation in UN-led peace talks in Geneva in protest at alleged government violations.

The peace talks were already shaky, having been threatened by fighting in the city of Aleppo.

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.

The Syrian government has accused rebel forces of violating the truce.

Russian Foreign Minister Sergei Lavrov insisted that the peace talks were "not frozen". He said a government delegation and other groups were still taking part.

Lavrov told a press conference in France that "external players" were trying to destabilise the talks and damage the Damascus government.