A senior Russian official says about 1,500 residents of Russia's North Caucasus are fighting alongside Islamic State militants in Syria and Iraq.

Sergei Melikov, President Vladimir Putin's envoy to the North Caucasus, says at least five militants who came back after fighting in Syria were killed in security sweeps last year.

Melikov said Thursday that the Islamic State group poses a "very serious threat" to the North Caucasus, Russian news agencies reported. He said efforts are needed to prevent young people from joining the ranks of militants.

Chechnya has become more stable under the watch of Kremlin-backed strongman Ramzan Kadyrov following two separatist wars, but the Islamist insurgency has engulfed other North Caucasus provinces. Melikov singled out Dagestan as the most volatile spot.