A suicide bomber killed at least two people and injured more than 11 outside a police station in the North Caucasus republic of Dagestan, a regional Interior Ministry spokesman said.
The exact number of victims has not been confirmed, with the latest Interfax report saying three people had died and 12 had sustained injuries.
Insurgents wage almost daily violence in the North Caucasus region to create an Islamic state in the predominantly Muslim are that neighbors the Black Sea resort city of Sochi, the site of the 2014 Winter Olympics.
Dagestan, which sits on the Caspian Sea, nearly 600 kilometers from Sochi, has become the focal point of violence that rights groups say is fanned by a combination of radical Islam and anger with corruption and human rights abuses.
The regional Interior Ministry spokesman said six police officers were injured, one of whom was in critical condition.
"The car exploded at the gates of the regional police station and, as a result of the explosion, nearby buildings collapsed. … Twenty people have been taken to the hospital," an unidentified source told Interfax.
The national anti-terrorism agency confirmed the bombing and said law enforcement agencies were being sent to the site. It gave no further details.
President Vladimir Putin has made the Sochi games a priority to showcase Russia's modern face and called on all law enforcement agencies to ensure safety in the region.
Material from The Moscow Times is included in this report.