By Tom Miles and Stephanie Nebehay
GENEVA (Reuters) - A round of Syria peace talks that ended on Thursday was a big missed opportunity but there may more talks next month if ideas can be found to encourage President Bashar al-Assad's government to engage, U.N. mediator Staffan de Mistura said.
He said neither side had actually "sabotaged" the latest talks by refusing to attend but he laid most of the blame for the failure of the round at the feet of the government side.
De Mistura voiced milder disappointment with the Syrian opposition, after they arrived in Geneva ruling out any future role for Assad. But he said that tough public stance had been tempered by a mature position in the closed-door discussions.
"The goal we had was to bring about real negotiations," de Mistura told a news conference. "Let me be frank. We did not achieve, we did not achieve these negotiations. In other words, negotiations in reality did not take place.
"I would conclude by saying (it was) a big missed opportunity. A golden opportunity at the end of this year when in fact there is a clear indication by many sides that the military operations are coming to a close," he added.
De Mistura said he was leaving Geneva for consultations in New York with U.N. Secretary General Antonio Guterres, followed by a meeting with the U.N. Security Council on Tuesday.
"I will probably need to come up with new ideas, parameters, about how to move the talks forward, particularly on constitution and elections," he said, adding that plans for a new round of Geneva talks in January depended on their outcome.
Civil war has ravaged Syria for more than six years.
Earlier, Syrian government negotiator Bashar al-Ja'afari accused the opposition, backed by Western countries and Saudi Arabia, of sabotaging the latest Geneva talks.
Ja'afari said Damascus did not want the talks to fail but the opposition had put down a precondition last month by concluding a conference known as "Riyadh 2" with a declaration that Assad had no role in Syria's political transition.
De Mistura said the Damascus government had wanted him to insist that the opposition withdraw the statement.
"That was not possible or a logical approach because to me it sounded like a precondition. The government engaged me with only on (discussions about) terrorism. The truth is there is not one single subject they accepted except that one."
(Reporting by Tom Miles and Stephanie Nebehay; editing by Mark Heinrich)