Russian President Vladimir Putin's jailed critic Alexei Navalny has been transferred out of his prison colony and moved to an unknown location, a top aide said Tuesday.

"Where Alexei is now, and which colony he is being taken to, we don't know," Leonid Volkov, Navalny's chief of staff, said in a statement on the Telegram app.

Earlier this year, Navalny had been added to a list of "terrorists and extremists," amid a clampdown on the opposition. Navalny and several of his allies, including key aide Lyubov Sobol, had appeared on a database of banned individuals compiled by the Federal Service for Financial Monitoring (Rosfinmonitoring).

The decision put them on a par with right-wing nationalist groups and foreign terrorist organizations, including the Taliban and the Daesh terrorist group.

The past year has seen an unprecedented crackdown on dissent in Russia, including the jailing of Putin's top critic Navalny last January and the outlawing of his political organizations.

Almost all of his top allies have since fled the country.

Navalny – Putin's most vocal domestic opponent – has been behind bars since returning to Moscow in January 2021 from Germany, where he was recovering from a poisoning attack with a nerve agent that he blames on the Kremlin.