A suicide bomber has blown himself up in the Chechen capital Grozny, also killing five police officers and wounding at least 12 other people.
The attack took place outside a hall where a concert marking Grozny's City Day was about to take place.
An interior ministry statement said police were searching a "suspicious" young man when he detonated a device.
Grozny was ravaged by two wars between Russia and Chechen separatists but has been relatively calm in recent years.
The Russian statement said that police officers on duty at the event "noticed a suspicious young man near metal detectors set up at the concert hall".
"When the police decided to search him and establish his identity, the man blew himself up," it said.
The bomber was identified as 19-year-old Opti Mudarov, a resident of Grozny.
The ministry said he had disappeared two months ago and had had no contact with his family since then.
There has been no information about any civilian casualties.
Analysis: Sarah Rainsford, BBC Moscow correspondent
This was a high-profile and symbolic target.
This year, Grozny City Day celebrations coincide with the birthday of Chechen President Ramzan Kadyrov.
He recently asserted that extremist Islamic insurgents - who carried out major bomb attacks in Russia in the run-up to the Winter Olympics - were no longer a threat in Chechnya, and no longer recruiting.
Mr Kadyrov claimed there were just "five to 12 bandits" left in the mountains.
The southern Russian republic of Chechnya saw two, brutal separatist wars in the 1990s that gradually morphed into a fight for an Islamic state in the region which is led by a group calling itself the "Caucasus Emirate".
This is the first major attack since the insurgents' long-time leader, Doku Umarov, was killed last year.
Russian Interior Minister Vladimir Kolokoltsev said he would decorate the police officers involved for preventing what it described as a major terrorist act.
"They gave their lives to save thousands of people who had come to the concert," Itar-Tass news agency quoted the ministry as saying.
Chechen leader Ramzan Kadyrov said the bomber "wanted to ruin people's joy on their day of celebration, but he has not succeeded".
The authoritarian leader also pledged to find and punish the perpetrators.