Syrian government forces backed by Russian air strikes committed a "massacre" of scores of civilians in Idlib governorate on Monday, part of a pattern of breaches of a two-week truce, opposition coordinator Riad Hijab told reporters on a teleconference.

Hijab said the latest fighting, as well as arrests by Syrian government forces, were causing the opposition to consider whether it should attend a round of peace talks in Geneva.

"It will be before the end of this week, there will be a clear decision about this," Hijab said.-Reuters