Russian news outlet Interfax is reporting that a suspect in Wednesday's St. Petersburg bombing was arrested on Saturday.
Interfax reported that "the organizer and direct perpetrator who triggered an improvised explosive device on December 27 in a supermarket in St. Petersburg was arrested during a special operation by the FSB," the Russian security service.
The report said the suspect was handed over to the Russian Investigative Committee for further action. No other details were given.
Wednesday's blast from a homemade bomb injured at least 13 people. Militant group Islamic State claimed responsibility for the blast, according to the SITE intelligence group, which monitors IS statements.
Russian President Vladimir Putin said Thursday that the attack was an act of terrorism.
Putin made the assertion at the Kremlin during an awards ceremony for Russian servicemen who served in Syria. He did not provide any further details.
Investigators initially said they were treating the case as an act of attempted murder.
Health officials said none of the victims suffered life-threatening injuries.