MOSCOW—President Vladimir Putin was front and center at the Group of 20 summit in Turkey, where he made his case for deeper international partnerships in fighting Islamic State after the Paris terror attacks.

“We proposed cooperation on antiterrorism; unfortunately our partners in the United States in the initial stage responded with a refusal,” Mr. Putin said. “But life indeed moves on, often very quickly, and teaches us lessons. It seems to me that everyone is coming around to the realization that we can wage an effective...