A post on Alexei Navalny's Twitter account on Friday said he had been moved from a jail in Russia's Vladimir region and his whereabouts were not initially known.

The Kremlin critic had been held in the Kolchugino detention center in the Vladimir region northeast of Moscow while in quarantine before serving his sentence in a penal colony.

What Navalny's team is saying

Navalny's team said on his Twitter account that his lawyers had been in Kolchugino since the beginning of the day. "Under various pretexts, they were not allowed to see Alexei," the account said. "Only at 2 p.m. were they told that Alexei had departed. They refused to answer where he went."

The account also retweeted similar comments made by Navalny's lawyer Olga Mikhailova to the commercial Russian radio station Echo of Moscow.

"We don't know where he is now," the station cited her as saying. "His whereabouts are unknown to us once again. The administration is supposed to notify relatives where he has been transferred. But, as practice has shown, this has not been done."

Nations demand protesters' release

The news came as dozens of countries called on Russia to release Navalny, saying his imprisonment was unlawful and demanding an investigation into his poisoning last year. They also called for hundreds of people arrested since protests against Navalny's detention earlier this year to be freed.

In a statement read out by Poland to the UN Human Rights Council in Geneva on Friday, signatories said actions against the opposition leader were "unacceptable and politically motivated."

"We call on the Russian Federation for the immediate and unconditional release of Mr. Navalny and of all those unlawfully or arbitrarily detained, including for exercising their rights to freedom of peaceful assembly and association, freedom of opinion and expression, and freedom of religion or belief," the joint statement said.

The 45 countries were mainly European but also included the US, Australia, Canada, and Japan.

A prominent critic of Russian President Vladimir Putin, Navalny was sentenced to two-and-a-half years in prison last month over alleged parole violations. These were linked to an embezzlement case that Navalny and his supporters say was trumped up for political purposes.

Earlier this month, the US and EU imposed sanctions against Russian officials and businesses over Navalny's poisoning with Soviet-era nerve agent Novichok.