The UN special envoy for Syria warned Tuesday that if troubled peace talks in Switzerland failed, then "all hope would be lost".

The UN special envoy for Syria warned Tuesday that if troubled peace talks in Switzerland failed, then "all hope would be lost".

"A failure is always possible, particularly after five years of horrible war," Staffan de Mistura said on Swiss television channel Radio Television Suisse.

"But if there is a failure this time, after two previous meetings in Geneva on Syria, then all hope will be lost," de Mistura said.

De Mistura is trying to coax representatives of the Syrian government and the opposition umbrella into indirect peace talks.

The negotiations have, however, after several days, failed to move beyond the preliminary stage, with the Riyadh opposition delegation on Tuesday cancelled a planned meeting with de Mistura, angry at what it called "unprecedented" Russian air strikes in Aleppo.

However many commentators consider such move by the opposition an attempt to cover up its confusion especially that up till now the delegation did not presented the names of the figures who will take part in the indirect talks with the Syrian Damascus.

For his part, chief government negotiator Bashar al-Jaafari stressed that the Syrian government will not accept the Riyadh Delegation’s preconditions, noting that the opposition was “not serious.”