United Nations mediator Staffan de Mistura expressed his disappointment on Thursday with the failure of the Geneva peace talks, describing them as a big missed opportunity. He said at the end of the talks that there may be a new round next month if new ideas can be found to encourage Bashar Assads regime to engage. "I will probably need to come up with new ideas, parameters, about how to move the talks forward, particularly on constitution and elections," de Mistura said, adding that plans for Geneva talks in January depended on the outcome of discussions at the UN in New York next week. “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 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. De Mistura said he was leaving Geneva for consultations in New York with UN Secretary General Antonio Guterres, followed by a meeting with the UN Security Council on Tuesday. Earlier, Syrian regime negotiator Bashar al-Jaafari accused the opposition of sabotaging the latest Geneva talks. Jaafari said Damascus did not want the talks to fail but the opposition had put down a precondition with a declaration that Assad had no role in Syria’s political transition. De Mistura said the regime 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 regime engaged me with only on (discussions about) terrorism. The truth is there is not one single subject they accepted except that one.” Later on Thursday, the Syrian opposition urged from Geneva de Mistura to openly declare the sides that were responsible for the failure of the negotiations. “The regime is challenging and undermining the international community,” said chief negotiator Nasser al-Hariri. “We are committed to the political solution to the conflict,” he added, but warning that “the Geneva talks are on the verge of collapse and the world should mobilize to save them.”