The strongman leader of Russia's Chechen republic says special operation units from his region have infiltrated the Islamic State group.

During a film teaser that aired on the Russian television channel Rossiya 1 on Sunday, Ramzan Kadyrov said Chechen special forces are fighting against the so-called Islamic State in Syria and have even infiltrated the group's ranks.

Kadyrov added that many extremist training camps were started by members of NATO states.

The Kremlin declined to comment on Kadyrov's claims.

Over 500 Chechen fighters are said to be fighting with IS in Syria. In the past, Kadyrov has offered Chechen fighters as ground troops in Syria.

The film about Chechnya's involvement in the Syrian conflict airs February 15.