The UN Syria envoy Staffan de Mistura said Wednesday he was "not expecting a breakthrough" at peace talks this week but voiced hope that rival sides could build "momentum" towards a deal.

"Am I expecting a breakthrough? No, I am not expecting a breakthrough," de Mistura told reporters on the eve of UN-brokered negotiations in Geneva, adding that he hoped this round could lead to further talks on a political solution to the six-year conflict.