Opposition leader says UN mediation in Syria conflict 'has failed'

A prominent Syrian opposition leader said on Thursday that United Nations mediation to end Syria's devastating six-year war had failed, vowing to continue the revolution against Bashar al-Assad's regime.

United Nations mediator Staffan de Mistura said earlier that the opposition must be "unified and realistic enough" to realize that they have not won the war, calling for a political process to end the conflict.

Riyad Hijab, chairman of the Saudi-backed High Negotiations Committee (HNC), rejected De Mistura's comments, saying his statements "reflect the defeat of UN mediation".

"The Syrian revolution continues," he said on Twitter, saying De Mistura had repeatedly made "un-studied" remarks on the conflict.

Hijab, a former Syrian prime minister under Assad, called for a new a UN "approach on the Syrian issue", without elaborating.

Assad has won a series of military victories but rebel groups still hold large parts of the northwest of the country and substantial enclaves in the southwest, in Homs province and near Damascus.

The remarks come ahead of a round of Syria talks between Damascus allies Russia and Iran and opposition backer Turkey in Astana next week.

The main opposition camp, the Saudi-backed High Negotiations Committee (HNC), has insisted that Syrian regime President Bashar al-Assad must leave office as part of any peace deal. 

That hardline stance has put the HNC at odds with two more moderate opposition groups, known as the Moscow and Cairo platforms

Several rounds of negotiations in Astana and a separate UN-sponsored track in Geneva between the government and the HNC have produced no visible progress on ending the war that broke out after a popular uprising in 2011.

Russia and Iran have stood by Assad, providing significant military backing to prop up his regime.

Some Western countries have softened their initial stance that he should leave power immediately, saying he could be part of a transitional period.