Donald Trump has offered his condolences to the victims of the St Petersburg metro explosion.
According to the White House the US President called his Russian counterpart Vladimir Putin on Monday to offer "the full support of the United States government in responding to the attack and bringing those responsible to justice."
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.