An unidentified assailant detonated an explosive device next to a patrol vehicle in Moscow early Tuesday, killing himself and a police officer, and leaving two other officers injured, officials said. The attack happened minutes after midnight near the Savyolovsky Train Station in the Russian capital’s downtown, according to Moscow’s branch of the Interior Ministry. It said the assailant approached a traffic police vehicle and detonated an explosive device, killing an officer on the spot and...