GENEVA - UN mediator Staffan de Mistura said on Wednesday that he expects no breakthrough at Syria peace talks starting on Thursday, but the beginning of a series of rounds of negotiations that aim to reach a political agreement."We are not having any excessive expectations, let's be frank," de Mistura told a news conference. He said he hoped to maintain momentum and that neither side would try to disrupt the talks by provoking the other. "I think it will be worthwhile. We are going to give it a serious try."While the Geneva talks will focus on politics, de Mistura said he expected more rounds of talks in the Kazakh capital Astana, convened by Russia, Turkey and Iran, to deal with the ceasefire and related humanitarian issues, including prisoners.He declined to discuss the format of the Geneva talks, which he said would start with bilateral meetings on Thursday, but did not say what his objectives were for this round.