Three people suspected of being linked to the bombing which left 14 people dead on the St. Petersburg subway were arrested by Russian security agents Thursday, Russian media reported..
The agents also deactivated an explosive device found at the suspects' apartment.
The three suspects all hail from the former Soviet Central Asia region, the same region as the suicide bomber who carried out the attack, 22-year-old Akbarzhon Dzhalilov, Russia's Investigative Committee stated.
No group has claimed responsibility for the attack, but Russian authorities are investigating whether Dzalilov trained with ISIS.
The explosive device which was deactivated Thursday contained materials used by Islamic militants in Syria, Fontanka.ru, a leading St. Petersburg news site, reported.