A United Nations rights expert said Monday that the "enforced disappearance" of Russian opposition leader Alexei Navalny was alarming, demanding that Moscow immediately release him.
The Kremlin critic's lawyers have been prevented from meeting him since December 6, and he did not appear for a scheduled court hearing last Friday.
"I am greatly concerned that the Russian authorities will not disclose Mr. Navalny's whereabouts and well-being for such a prolonged period of time which amounts to enforced disappearance," said Mariana Katzarova, the UN Special Rapporteur on human rights in Russia.
Navalny, 47 -- who has been a thorn in the side of Russian leader Vladimir Putin -- was jailed for 19 years on extremism charges in 2021 after surviving a poisoning assassination attempt.
Katzarova said she had raised her concerns with the Russian authorities after Navalny's team were told on Friday that he had been removed from the Vladimir region near Moscow on December 11 and taken to an undisclosed location.
Navalny's family and lawyers had sent letters to all penal colonies trying to identify his whereabouts, she said.
"They have received initial information that he might be at an Omsk penal colony, but that information was later rejected," Katzarova said in a statement.
A court earlier this year ruled that Navalny be moved to a harsher prison.
Katzarova said the extremism charges he was convicted of were "baseless" and warned that detainees face high risks of serious rights violations during transportation.
The independent expert, who was appointed by the UN Human Rights Council but who does not speak on behalf of the UN, insisted that "the term 'extremism' has no basis in international law".
"When it triggers criminal liability it constitutes a violation of human rights."
Her statement slammed "the unrelenting criminal persecution of Mr. Navalny", which had been "widely condemned internationally, indicating blatant abuse of the court system for political purposes."
She said three of Navalny's lawyers were arrested in October, also on extremism charges, and now risked lengthy imprisonment themselves.
"I call on Russian authorities to abide by their international human rights obligations," Katzarova said.
"Mr. Navalny and all those arbitrarily detained should be released immediately and provided remedies and reparations for all the harm suffered."