Gunmen opened fire at a synagogue, an Orthodox church and a police post in attacks across two cities in Russia's North Caucasus region of Dagestan on Sunday, killing an Orthodox priest and multiple police officers, the region's head said.

"This is a day of tragedy for Dagestan and the whole country," Sergei Melikov, governor of the Dagestan region, said in a video published early Monday on the Telegram messaging app.

Melikov said that more than 15 police officers "fell victim" to what he said was a "terrorist attack," but he did not specify how many of the police were killed and how many were injured. Russia's Interfax agency reported that at least 15 police officers were killed.