U.S. Secretary of State John Kerry raised concerns with Moscow this week about reports of Chechens and other fighters crossing into Ukraine from Russia to join the rebellions against the leadership in Kiev.
Chechen leader Ramzan Kadyrov, who fought Russian troops in the North Caucasus province in the 1990s, echoed Moscow's denials of involvement but said he had recognized some of the fighters in pictures from Ukraine.
"We did not send them. They are absolutely not our staff," he said in an interview to be shown on Russian television on Saturday.
"If a person voluntarily leaves (Russia), we have no right to stop him. This is his own decision."