The attacks across the cities of Makhachkala and Derbent in the country’s Russia’s Northern Caucasus came three months after 145 people were killed in an attack claimed by the Islamic State on a concert hall near Moscow. “This is a day of tragedy day for Dagestan and the whole country,” Sergei Melikov, governor of the Dagestan region, said in a video published early on Monday on the Telegram messaging app.