The St Petersburg subway bomber has been identified as a Kyrgyzstan-born Russian citizen, according to Kyrgyz security services.
The Kyrgyz intelligence agency said the suspect was born in Osh, the country's second largest city, in 1995.
Kazakhstan's security services said it was working with Russia to investigate Monday's blast, which killed 11 people.
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.