Kadyrov, who has led the North Caucasus region of Chechnya since 2007, made the claims in a preview of a documentary set to air on state television tommorrow.
The documentary claims that "agents from special forces from Chechnya were embedded" in IS training camps to collect intelligence and help identify targets for Russian air strikes.
Quoting Kadyrov, it said that the "best fighters" from mostly Muslim Chechnya have managed to create an "intricate agent network directly inside IS," although some have been killed.
"But they knew where they were going, what they were getting involved in. They went there so we can live peacefully in Chechnya and all over Russia."
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The preview showed Kadyrov at a training camp in Chechnya where heavily-armed men were shooting at targets and completing obstacle courses.
Chechen agents in the IS group "gather information about the structure and numbers of the terrorists and set targets for bombings," the documentary claimed.
There was no way to immediately verify Kadyrov's claims. Russian President Vladimir Putin has ruled out a ground operation in Syria.
A source in the Chechen leadership told Interfax news agency today that "there have been people from Chechnya in the conflict zone on the territory of Syria and Iraq since the emergence of IS."
"These consist of self-organised groups of young men who aim to fight the terrorist organisation," the source said, adding that "none of them are members of the Russian armed forces or working for the interior ministry."
IS fighters in December released a video showing the beheading of an ethnic Chechen man who had made a filmed confession that he worked for Russian special services to spy on IS in Syria.
At the same time, some Muslim Chechens and other Russians have gone to Syria to support the IS jihadists.
According to figures released by Russia's FSB security service in December, nearly 2,900 Russians are fighting or have fought with the extremists in Iraq and Syria.