Some 200 Russian Islamists who back North Caucasus insurgents are fighting in Syria for al-Qaeda, the head of the Russian security service (FSB) said Thursday, Russian news agencies reported.

"The fact that around 200 fighters from Russia are fighting on the side of the Caucasus Emirate under the flag of al-Qaeda and other related structures provokes concern in Russia," the head of the FSB Alexander Bortnikov said at an international security forum in the central Russian city of Kazan.