Six nationals of Central Asian countries were detained following a series of anti-terrorism raid by Russia's Federal Security Service (FSB) the Interior Ministry and National Guard in St. Petersburg, the Investigative Committee said in a statement.
The detainees are suspected of being active since November 2015 in recruiting other Central Asian immigrants for "terrorist activity", and for ISIS and another banned Islamist movement, Fateh al-Sham, previously known as the Nusra Front.
Searches are being conducted at the suspects' places of residence; law enforcement officers are seizing extremist literature, document and other items significant to the case, investigators said.
While the investigation does not establish a connection between the detainees and the suicide bomber in the St. Petersburg metro, the examination continues.
"As for Akbarzhon Dzhalilov, who, according to the investigation data, set off an explosive device in the train's vehicle, his identity has been confirmed by the results of a DNA test", the committee's spokeswoman Svetlata Petrenko said. The identification of Kyrgyz-born Akbarzhon Jalilov as the bombing suspect stoked fears of police action targeting migrants from Central Asia and the Caucasus.
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Jalilov allegedly detonated an explosive on the city's metro between the central Sennaya Square and Tekhnologichesky Institut stations.
Islamic State - which has fighters from ex-Soviet Central Asia among its ranks - has repeatedly threatened to attack Russian Federation in revenge for Moscow's backing of Syrian leader Bashar al Assad.
Offering condolences to the victims of the St. Petersburg attack, Mirziyoev said "for all of us terror has no borders and no ethnicity". Dzhalilov's DNA was found on the bag.
An unidentified device went off at about 2:40 Moscow time on April 3 in a subway train vehicle when it was moving from the Tekhnologichesky Institut Station to the Sennaya Ploshchad Station. Jalilov had lived in Russia for several years and was a Russian citizen.
"We know that each of our countries, practically every one, is a possible and potential target of terrorist attacks".