Dagestan: Gunmen open fire against Orthodox churches and Synagogue - Death toll at 17 and rising

"It is a tragic day for Dagestan and the entire country," Sergei Melikov said in a video message shared via the Telegram platform.

The figure of more than 15 police officers killed was given by Mr Melikov. He also said several civilians had lost their life, including a priest, Father Nikolai Kotelnikov, who he said had served in Derbent for more than 40 years.

The coordinated attacks by gunmen in Dagestan's capital, Makhachkala, and the city of Derbent (further south), came three months after a massacre in which 145 people died at a concert hall near Moscow was claimed by the Islamic State group.

So far there has been no claim of responsibility for the attacks in Dagestan.

"We understand who is behind the organization of the terrorist attacks and what their goal was," Melikov noted, but did not elaborate further.

Russian media reports report information from sources in the security services, according to which two of the sons of Magomed Omarov, head of the Sergokalinsky district, were among the perpetrators. Omarov, 63, was arrested and is suspected of organizing the terrorist attack.

Six of the attackers were killed, according to Sergei Melikov, who declared three days of mourning in the Republic of Dagestan.