SEOUL, South Korea – With Russian President Vladimir Putin de facto confirming multiple signals of a North Korean troop presence in Russia and indications rising of their deployment to the war-torn Kursk oblast, Seoul is caught in a bind. Russia’s State Duma on Thursday ratified a North Korean-Russian strategic partnership that was agreed in Pyongyang in June. On the same day, Mr. Putin addressed the issue of images of North Korean troops in Russia that have appeared online. Though North Korea’s United Nations representative in New York called the troop deployment claims “groundless rumors,” Mr. Putin, speaking at a press...