The head of Al-Qaeda's Syrian affiliate has called on jihadists in the Caucasus to attack Russian civilians and soldiers in retaliation for Moscow's air strikes in Syria.

"If the Russian army kills the people of Syria, then kill their people. And if they kill our soldiers, then kill their soldiers. An eye for an eye," Abu Mohamed al-Jolani, the head of Al-Nusra Front, said in an audio recording released late Monday.