At least 20 people were reportedly killed in the attacks by armed groups against multiple facilities in Russia's southern republic of Dagestan.

Local health authorities said police officers were among those killed, and that 26 people were wounded.

Russian authorities are investigating the incidents as terrorist attacks.

Armed groups attacked Russian Orthodox churches, synagogues and police officers in the cities of Makhachkala and Derbent on Sunday.

Russia's National Antiterrorism Committee says five assailants were killed.

Independent Russian media and the US Institute for the Study of War have reported that supporters of a local organization affiliated with the Islamic State group praised the attacks on social media.

Russia's spokesperson Dmitry Peskov on Monday said President Vladimir Putin expressed condolences to the victims' families. He emphasized that Russian society would not be destabilized.

Russia had stepped up security measures after a terrorist attack at a concert hall in the outskirts of Moscow killed more than 140 people in March. The Putin administration is believed to be deeply concerned over its failure to prevent the latest attacks.