The data comes a week after the terrorist attack in Moscow, where more than 130 people were killed.
Another nine arrested
Earlier on Friday, nine people in Tajikistan were said to have been arrested on suspicion of involvement in that act, according to consistent sources in international media and state-run channels in Russia.
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The arrests are said to have taken place in a suburb of the capital Dushanbe and the suspicions are said to consist of having “contacts” with the main suspected terrorists or the extremist movement IS.
The four main suspects in custody in Moscow are originally from Tajikistan, a heavily governed and traditionally pro-Russia country in Central Asia. IS has long been reported to also recruit many Tajiks.