Up to 5,000 Russian citizens may be fighting for the international terrorist organization, Islamic State of Iraq and the Levant (ISIL), CIS Antiterrorism Center head Police Lt. Col. Andrei Novikov has said.

"According to the security services, about 2,000 holders of Russian passports are fighting for ISIL. Some experts believe their actual number may near 5,000," Novikov told Interfax in an interview.

In his words, some information concerning these Russian citizens has been confirmed with documentary evidence, and some is still being verified. Security services and law enforcement authorities of all CIS member countries are doing this work, he said.

"We need to apply our agents and technical control means," the CIS Antiterrorism Center head stated.