A group supporting jailed Russian opposition leader Alexei Navalny says he is being held in a prison colony above the Arctic Circle.

The critic of President Vladimir Putin's administration was poisoned in a case suspected to involve the Russian government. He was treated in Germany. On returning to Russia in 2021, he was arrested in connection with a past economic incident. He was sentenced and imprisoned at a facility in the vicinity of Moscow.

His support group said in a social media post on Monday that Navalny was located in a prison colony in the Yamalo-Nenets Autonomous District, northern Russia. The group had been trying to determine his whereabouts since it lost contact with him on December 6.

A lawyer who visited Navalny in the colony said he is fine.

Early this month, Navalny launched a campaign through his support group to urge people to vote for any candidate other than Putin in the presidential election in March next year.

The prison colony, situated north of the Arctic Circle, is known as among the toughest prisons in Russia.

One of Navalny's aides said on social media that it is almost impossible to even send letters there, and that this is the highest possible level of isolation from the world.