Russian police arrested three people Thursday in connection with a suicide bombing in the St. Petersburg subway system earlier this week.

Police said the suspects come from the same region of central Asia as the bomber, Akbarzhon Dzhalilov. A bomb also was found and disarmed in the apartment shared by the three suspects on the outskirts of St. Petersburg.

The Investigative Committee, Russia’s top criminal investigation agency, said investigators found other evidence in the apartment that will help in the case against the three suspects.

Reuters reports the unexploded bomb found in the apartment was similar to the unexploded bomb found Monday in the subway.

The arrests come a day after eight other central Asian men were arrested in St. Petersburg for allegedly recruiting people to join the Islamic State and other extremist groups.

The poverty-stricken countries in Central Asia have become a prime recruiting territory for the militant groups, with thousands of people from the region believed to be fighting alongside the IS group in Iraq and Syria.

Authorities said there is no immediate evidence linking the alleged recruiters to the subway bombing.

No one has yet claimed responsibility for the suicide bombing Monday that left 14 people dead, including the bomber, and more than 50 others wounded.