A Turkish security official says the suicide bomber accused of the deadly attack on the subway in the Russian city of St. Petersburg was deported from Turkey in 2016.
A woman places flowers in honour of the victims of the April 3 blast on the platform of Technological Institute metro station in Saint Petersburg on April 4, 2017.
The FSB said it detained the man - named as Abror Azimov - today in the Odintsovo suburb of Moscow, describing him as "originally from Central Asia", in a statement quoted by RIA Novosti news agency.
Azimov is believed to have trained the perpetrator of the bombing, Akbardzhon Dzhalilov, who left the explosive device in the train and was also killed in the explosion.More news: Pence left to fill policy gaps in trip to South Korea, Japan
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The operation by the FSB was made in the region of Odentsov, province of Moscow.
The suspect has been taken for questioning to the Investigative Committee, which probes serious crimes, the FSB said.
Russia's Federal Security Service has detained a person who could have been involved in the explosion in the St. Petersburg Metro, as part of the criminal investigation launched by the Investigative Committee, the center said in a statement, RT reports. Earlier Russian media reported that the bomber had made a telephone call to someone in Moscow before the attack.