Russia President Vladimir Putin has laid a floral tribute at a impromptu memorial to the victims of a bomb blast on the St Petersburg metro station.
Mr Putin happened to be in Russia's second-largest city for a meeting with his Belarusian counterpart Alexander Lukashenko when the explosion took place.
The seven people were from Central Asian countries and investigators say they were recruiting for IS.
The bombing of a subway train in Russia has drawn condemnation from world leaders.
A blast has ripped through an underground train in Russia's second-largest city on Monday.