Thousands of Cossacks will help police patrol southern Russia during the 2014 Winter Olympics in the Black Sea resort of Sochi to keep Muslim immigrants out.

The Cossacks, an effective military force in czarist times, will be charged with helping police prevent migrants crossing over from the neighbouring Caucasus to take advantage of an expected jobs bonanza.

The deployment has been criticised because it will inflame ethnic tensions and could encourage hate crimes against Muslims.

The Cossacks will not be armed but will bear insignia clearly showing they are part of a military force, the Associated Press reported.

Konstantin Perenishko, deputy head of the Kuban Cossack Army, said they will focus on migrants whose "behaviour is not always legal, not always right".

The mission was formally announced by governor Alexander Tkachyov in a speech to police officers.

"What you can't do, a Cossack can," Tkachyov said.

Tkachyov warned that the Cossacks would not be under as much scrutiny as the police.

"The police have sufficiently high powers but there are limitations," the governor said. "We have seen this in recent years because of democracy and the greater attention paid to human rights and civil society."

The region has grown increasingly unstable since the start of the first Chechen separatist war in 1994 as it faces economic problems and an Islamic insurgency.

Ethnic tensions have increased in Russia in recent years, with Caucasian natives and migrant workers from the former Soviet republics often facing discrimination.