Russia's top security agency says it has been investigating 1,600 individuals and legal entities suspected of aiding the Islamic State group.

Alexander Bortnikov, director of the Federal Security Service, the main KGB successor agency, also said Tuesday that his agency has identified 2,900 Russian citizens suspected of involvement in extremist groups in Syria and Iraq.

He said that 198 of them have been killed in fighting and another 214 have returned to Russia. Bortnikov added that 80 of those who have come back have been convicted and another 41 have been arrested.

President Vladimir Putin has said previously that between 5,000 and 7,000 citizens of Russia and other ex-Soviet nations have joined the IS. He said that Russian air campaign in Syria has been aimed at protecting Russia's security.