Alexei Navalny is being moved to a hospital as he enters the third week of his hunger strike over what he called inadequate medical treatment in a Russian prison.
The Russian state penitentiary service confirmed on Monday that a decision had been made to transfer the imprisoned opposition leader to a hospital for criminals located in another penal colony in Vladimir, a city 180 kilometres (110 miles) east of Moscow.
According to the statement, Mr Navalny’s condition is deemed "satisfactory" and he has agreed to take vitamin therapy.
The announcement comes two days after the 44-year-old’s physician said Mr Navalny’s health was deteriorating rapidly and that he could be on the verge of death.
Dr. Yaroslav Ashikhmin, said on Saturday that test results he received from Mr Navalny’s family show sharply elevated levels of potassium, which can bring on cardiac arrest, and heightened creatinine levels that indicate impaired kidneys.
"Our patient could die at any moment," he said in a Facebook post.
The campaigner is currently serving two-and-a-half years at the IK-2 penal colony prison on a 2014 embezzlement conviction he said was fabricated and the European Court of Human Rights deemed to be "arbitrary and manifestly unreasonable."
He went on a hunger strike on March 31, demanding access to proper medication and a visit from his doctor after experiencing severe back and leg pains.
He also said he was effectively deprived of sleep because a guard checks on him hourly at night.
In a message from prison on Friday, Mr Navalny said prison officials threatened to force-feed him "imminently," using a "straitjacket and other pleasures."
In response to the concerning news about Mr Navalny’s health this weekend, his allies have called for a nationwide rally on Wednesday, the same day that President Vladimir Putin is scheduled to give his annual state of the nation address.
On Monday, Russia's Interior Ministry called on the population not to take part in planned protests this week.
The ministry said: “Any aggressive actions by participants in unauthorised public meetings, especially attempts to provoke clashes with law enforcement officials, will be regarded as a threat to public safety and immediately suppressed."
Meanwhile, the US has warned Russia there would be "consequences" if Mr Navalny were to die in jail.
The UK, France, Germany and the European Union also stated their concern over his treatment and demanded his release.
Mr Navalny returned to Moscow in January after spending five months in Germany recovering from a near-fatal nerve agent poisoning he blames on the Kremlin - accusations Russian officials have rejected.