A lawyer for jailed Kremlin critic Alexei Navalny said he was now at a prison hospital at a penal colony in the town of Vladimir near Moscow, following a decision by authorities to transfer him earlier today.
Alexei Liptser said he was waiting at the penal colony to visit his client but had yet to be allowed in.
Navalny began refusing food on last month in protest at what he said was the refusal of prison authorities to provide him with adequate medical care for acute back and leg pain.
He was imprisoned in February for more than two years on old embezzlement charges.
It came just weeks after he returned to Moscow from Germany where he had been recuperating from a near-fatal poisoning attack.
The prison service said in a statement that a group of doctors had "made a decision to transfer A Navalny to hospital for convicts located on the territory of Penal Colony No 3".
"At present, A Navalny's medical condition is deemed to be satisfactory; he is being examined by a general practitioner every day," the statement added.
The 44-year-old anti-corruption campaigner was sentenced earlier this year to serve out his sentence in Penal Colony No 2 outside the Russian capital.
He soon after began complaining of back pain and numbness in his limbs.
On 31 March, Navalny announced a hunger strike to demand proper medical treatment and his allies said the prison authorities have threatened to begin force feeding him.
The prison service said in its statement that with Navalny's consent, "he was prescribed vitamin treatment".
Western countries have urged Russia to provide Navalny with proper medical care and to release the Kremlin critic, and warned against possible repercussions.
EU foreign policy chief Josep Borrell said the bloc holds Russia "responsible" for Navalny's health as EU foreign ministers held virtual talks on increasing tension with Russia.
However, the Kremlin today dismissed concerns from Western countries over Navalny's health.
"The health of convicts in the Russia Federation cannot and should not be a topic for their interests," said Kremlin spokesman Dmitry Peskov, referring to Western countries, adding that, "we do not monitor the health status of Russian prisoners".