Alexei Navalny, Russia's most prominent opposition politician, is suffering from a mystery ailment in jail that could be some sort of slow acting poison and has lost 8kg in weight in just over two weeks, his spokeswoman said.
An ambulance was called last weekend for Mr Navalny to the maximum-security IK-6 penal colony at Melekhovo, about 250km east of Moscow, where he is being held, Kira Yarmysh said in a video clip on Twitter accompanied by disturbing background music.
The spokeswoman added that an unknown stomach complaint had flared up on Friday and that prison doctors had treated him in the past by injecting him with medicine which they had refused to identify.
"We do not rule out that at this very time Alexei Navalny is being slowly poisoned, being killed slowly so that it attracts less attention," Ms Yarmysh said in the Twitter post.
"He is being held in a punishment cell with acute pain without medical help."
There was no immediate comment from Russia's federal penitentiary service which has in the past denied allegations that its employees have mistreated him and have said he has always been afforded medical treatment when needed.
Mr Navalny, who is serving combined sentences of 11-and-a-half years for fraud and contempt of court on charges he says were trumped up to silence him, said via Twitter on Tuesday that he had been moved back into solitary confinement and forced to endure "extremely hellish" conditions.
Ms Yarmysh said he had suffered similar stomach pain in January after being treated with antibiotics for a virus and had again lost a lot of weight.
Mr Navalny is a former lawyer who rose to prominence more than a decade ago by lampooning President Vladimir Putin's elite and voicing allegations of corruption on a vast scale.
His supporters cast him as a Russian version of South Africa's Nelson Mandela who will one day be freed from jail to lead the country.
Conversely, Russian authorities view him and his supporters as extremists with links to the CIA intelligence agency in the United States intent on trying to destabilise Russia.
They have outlawed his movement, forcing many of his followers to flee abroad.
In 2020, Mr Navalny survived an apparent attempt to poison him during a flight in Siberia, with what Western laboratory tests determined was a nerve agent.
He accused the Russian state of trying to kill him, something it denied.
Mr Navalny was treated for that poisoning in Germany but voluntarily returned to Russia in 2021, where he was arrested on arrival and jailed.
Ms Yarmysh said medicine sent to the prison by his mother was not collected by prison officials from the post office and was returned.
His supporters had to battle with the prison authorities every time he fell ill to ensure he received some kind of treatment, she said.
"Abusing Alexei's health is a regular practice of (prison) colony number six. All we can do right now (to help him) is to talk about Alexei everywhere," said Ms Yarmysh.
