"The support of Plotnitsky [leader of the self-proclaimed Luhansk People's Republic] is what they did at the initial stage," Hrytsak said.

"The liquidation of opposition-minded leaders and militants of illegal armed groups, the forced reorganization of Russian Cossack and other formations – we have got many documents on this and reports documenting how they were disarming gangs, how they were eliminating Aleksandr Bednov (nom de guerre "Batman"), "Foma," "Kosogor," and others," the official added.

Read alsoSBU chief praises tightening entry rules for foreigners, suggests criminal penalty for MPs visiting RussiaWhat is more, members of PMC Wagner committed sabotage and provocative actions against the Ukrainian forces of the Anti-Terrorist Operation (ATO) along the contact line in Donbas. Thirty-six mercenaries have been killed, Hrytsak said.

As UNIAN reported, Hrytsak said earlier that the SBU had established the involvement of PMC Wagner in armed conflicts in Donbas and Syria.

"To date, we have identified 1,587 people who are members of PMC Wagner. The total number we see now is about 5,000 people. The geography of their deployment is Ukraine (occupied areas in Donbas; June 2014-August 2015) and Syria (the cities of Homs, Hama, Latakia, Damascus, and Palmyra on August 15, 2015), the SBU's chief said.

The Wagner's training base is located in Krasnodar Krai, Russia.

According to Hrytsak, "this project of the Russian special services allows the Kremlin's politicians to confidently state before the public and the international community: 'They [Russian military] are not there [in Ukraine]' or 'We have not sent them there.'"