Members of an armed group opened fire in two cities in the southern Russian republic of Dagestan, resulting in a number of casualties.
Gunmen attacked a synagogue, two Orthodox churches and a police post in Derbent and Makhachkala on Sunday.
A Jewish organization says the attackers set fire to the synagogue. Video footage from the site shows the building in flames, with plumes of smoke rising from it.
Russian media reports say at least nine people, including police officers and those at the church, have been killed and many others injured.
It is not known what was behind the attack and nobody has claimed responsibility for it.
The Russian Investigative Committee has opened an investigation into what it believes to be a terrorist attack.
Last October, protesters in opposition to Israeli military attacks on the Gaza Strip stormed an airport in predominantly Muslim Dagestan when a passenger plane arrived from Israel.
Russian authorities have carried out counterterrorism operations in Dagestan and detained Islamic extremists following a terrorist attack at a concert hall on the outskirts of Moscow in March.