Alexei Navalny

Jailed Putin critic 'moved out of Moscow prison'

He was taken from the remand prison without any notification being given to his supporters and may have been sent to a prison camp, they added.

Earlier this month a Moscow court converted a 2014 suspended sentence for embezzlement into a prison term.

The original conviction was widely seen as politically motivated.

Navalny is the most ferocious critic of the Russian authorities under President Vladimir Putin.

Russian opposition leader Alexei Navalny detained on arrival in Moscow

He flew from Berlin to Moscow, arriving in Russia for the first time since he was nearly killed by a nerve agent attack.

The activist says the authorities were behind the attempt on his life, an allegation backed up by investigative journalists but denied by the Kremlin.

Russia's FSIN prison authority confirmed that officers had detained him, the Interfax news agency reported.

Metal barriers were erected inside the airport, Vnukovo, and Russian media reported that several activists - including key Navalny ally Lyubov Sobol - had been detained there.

Alexei Navalny: Putin critic 'probably poisoned' - doctors

The Charité hospital released a statement saying "clinical evidence suggests an intoxication through a substance belonging to the group of cholinesterase inhibitors".

But doctors who treated him in Russia say the substance was not present.

Mr Navalny fell ill on an internal flight in Russia on Thursday.

Video appeared to show Mr Navalny, a dogged critic of the Kremlin, writhing in agony on the flight from Tomsk in Siberia to Moscow.

His supporters suspect poison was placed in a cup of tea he drank at the airport in Tomsk.

Jailed Russian opposition head develops 'allergy'

Officials gave no details of his condition but Mr Navalny's spokeswoman said he had had an allergic reaction with severe facial swelling - something she said he had not experienced before.

A hospital source told Russian media his condition was satisfactory,

An eye doctor who treated Mr Navalny previously is concerned he may have been injured by a chemical substance.

Mr Navalny was jailed for 30 days last week after calling for unauthorised protests, which took place on Saturday.

Russia protests: Opposition leader and hundreds others arrested

Thousands of people joined rallies nationwide, calling for the resignation of Prime Minister Dmitry Medvedev over corruption allegations.

At least 500 other protesters were detained in the capital and across the country.

Most of the marches were illegal, organised without official permission.

TV pictures showed demonstrators chanting "Down with [Russian President Vladimir] Putin!", "Russia without Putin!" and "Putin is a thief!".

Correspondents say the marches appear to be the biggest since anti-government demonstrations in 2011/2012.