A large group of ISIS (Islamic State of Iraq and Syria) followers detained in Ukraine are Russian citizens, Chief of the Security Service of Ukraine (SBU) Vasyl Hrytsak said on Wednesday.

"Recently there have been several special operations in Ukraine, during which we raided four transit centers used by ISIS to relocate their supporters (in Europe), as well as to Syria. Of the 25 detained foreigners, 19 are citizens of the Russian Federation," Hrytsak said in an interview with TV Channels on March 23.

"What does it mean? It means that from Russia or some post-Soviet space representatives or followers, members of ISIS are moving over Russia's territory. They use the territory of Ukraine as a transit zone," the SBU chief said.

Hrytsak said he is unfamiliar with reports about the success of Russian security services in detaining ISIS followers on the territory of the Russian Federation.