As the residents of Russia's second-largest city try to regain their nerve in the wake of a fatal subway bombing, officials announced that six people have been arrested on suspicion of recruiting terrorists.
The statement from the Investigative Committee gave few details, but said those arrested came from Central Asian countries that once were part of the Soviet Union.
Officials have said the suicide attacker behind Monday's blast that killed 14 people in St. Petersburg was a native of the Central Asian country of Kyrgyzstan.
There was no immediate information tying those arrested with the suspected bomber, identified as 22-year-old Akbardzhon Dhzalilov.
Fifty-five people wounded in the blast remain hospitalized, deputy mayor Anna Mityanina said Wednesday.
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The predominantly Muslim Central Asian states are seen as a prime recruiting ground for Islamic militants.
Meeting with the heads of security services from a regional alliance that includes most of Russia's Central Asian neighbors, President Vladimir Putin warned that terrorism remained a threat to all in the region.
"We see that, unfortunately, the situation is not improving," he said. "The recent tragic events in St. Petersburg are the best confirmation of this. We know that each of our countries, practically every one, is a possible and potential target of terrorist attacks."
Earlier Wednesday, the Investigative Committee said in a statement they searched the home of Dhzalilov in St. Petersburg. They also examined CCTV footage from outside Dzhalilov's home which shows him leave home with a bag and a backpack.
The bomb went off on a train under Russia's second-largest city on Monday. Another bomb, hidden in a bag, was found and de-activated at another St. Petersburg station just half an hour before the blast. Dzhalilov's DNA was found on the bag.
