Russian police Col.-Gen. Andrei Novikov, told newsmen that authorities confirmed that a minimum of around 2,000 Russian passport holders had joined the extremists army in Iraq and Syria.
In southern Russia, several, mostly Muslim regions at the edge of the Caucasus Mountains, have been coping with a simmering Islamist insurgency for decades.
Several of the Emirate’s members were shown in videos late last year declaring allegiance to the Islamic State around the time of a terrorist attack in Chechnya that the group took credit for.
The Caucasus rebels, battle-hardened by two separatist wars with Russia, are rumored to be some of the Islamic State’s most successful fighters.
Red-bearded Caucasus rebel, Tarkhan Batirashvili, whose combat name is Omar al-Shishani, is believed to be an IS commander in Syria, with a series of decisive victories attributed to him.
Novikov warned that the IS might have obtained nuclear material capable of making a bomb that would cause “worldwide panic.”
However, he did not say how the material could have been obtained.
The IS said in May in its online propoganda magazine, Dabiq, that it could buy a nuclear weapon from the predominantly Muslim nation of Pakistan.
It added that IS allegedly helped North Korea obtain atomic arms in the 1990s.