GENEVA — The eighth round of Syrian peace talks brokered by the United Nations fizzled to a close on Thursday without progress toward a deal to end seven ruinous years of war, and with the chief mediator saying that the Syrian government was not “really looking to find a way to have a dialogue.”

The United Nations mediator, Staffan de Mistura, had called the parties to Geneva hoping for the first “real negotiations” in two years, but he acknowledged to reporters that “negotiations in reality did not take place.”

The two-week exercise, he said, was a “golden opportunity missed.”

Mr. de Mistura said he planned to convene another round of talks in Geneva in January but needed an infusion of new ideas and would sound out the major powers when he briefs the United Nations Security Council in New York on Tuesday.