More than 15 police officers and several civilians, including an Orthodox priest, were killed by armed militants in Russia’s southern republic of Dagestan on Sunday, its governor Sergei Melikov said in a video statement early Monday.

The gunmen opened fire on two Orthodox churches, a synagogue and a police post in two cities, according to the authorities. Russia’s National Anti-Terrorist Committee described the attacks in the predominantly Muslim region with a history of armed insurgency as terrorist acts. Monday, Tuesday and Wednesday were declared days of mourning in the region.