Russia is investigating possible terrorism after a 17-year-old boy blew himself at a Federal Security Service office in the north of the country.
Russia's Investigative Committee said the teenager, believed to be a local boy, detonated a homemade bomb in the lobby and died on the spot.
Three FSB employees were said to have been wounded in the blast.
The bomber's motive is not yet clear, but Russian media is reporting on an unconfirmed warning posted by the teenager on social media.
According to the reports, he described himself as a communist anarchist and said he had decided to act because the FSB was fabricating cases and torturing people.