Kremlin critic Alexei Navalny has been transferred to the Vladimir region some 200 kilometres (124 miles) east of Moscow to serve a 2.5-year term in a penal colony, Moscow's public commission that monitors detainees' human rights said Sunday.

President Vladimir Putin's most prominent opponent was sentenced this month to 2.5 years in a penal colony for breaching parole terms while in Germany recovering from a poisoning attack.

For several days, his allies had been unaware of his whereabouts, with the head of the Federal Prison Service saying Friday Navalny had been transferred from a Moscow detention centre to a penal colony without providing further details.

Reports based on unnamed sources circulated in local media over the weekend about Navalny's possible location, before Moscow's public commission said in a statement Sunday that the opposition figure was in a Federal Prison Service institution in the Vladimir region.

' We have 100 percent information that Navalny arrived in the Vladimir region to serve his sentence,'  a member of the commission, Alexei Melnikov, told the Inferfax news agency.

' At first, he will be in quarantine, then he will be transferred to his colony,'  he added.

Navalny spent months recovering in Germany from the near fatal poisoning with the Soviet-era nerve agent Novichok that he claims was ordered by Putin. The Kremlin has repeatedly denied the claim.

The 44-year-old opposition politician was arrested on his return to Moscow last month, sparking a wave of protests across the country and a brutal police crackdown.

Leaders of Western countries have condemned his detention and called for his immediate release.

The European Union has agreed to impose sanctions on four senior Russian officials over the crackdown.