At least 4,500 Russians have left the country to fight with "terrorists" in the Middle East, North Africa and other regions, the head of the FSB security service, Alexander Bortnikov, said on Tuesday.

Speaking in an interview with government newspaper Rossiiskaya Gazeta, Bortnikov said that "as of today, some 4,500 Russians had been identified to have gone abroad to take part in fighting on the side of terrorists."

Bortnikov said the security service worked to prevent militants from the Middle East, North Africa, Pakistan and Afghanistan from coming to Russia and stopping Russians from going there.