LAUSANNE, Switzerland—A meeting of top diplomats from nine nations, including the U.S., Iran, Saudi Arabia and Russia, ​produced new ideas to end the violence in Syria but no concrete agreements or a definitive pledge to meet again.

After more than four hours of talks on Saturday, which also included foreign ministers from Turkey, Qatar, Jordan, Iraq and Egypt, as well as the U.N.’s special envoy to Syria, Secretary of State John Kerry said the sides hadn’t found a way to resume aid deliveries or restore calm. But he said...