Several doctors have been prevented from seeing Russian opposition leader Alexei Navalny in a prison hospital after his three-week hunger strike.

Mr Navalny was transferred on Sunday from a penal colony east of Moscow to a prison hospital in Vladimir, a city 180 kilometres (110 miles) east of the capital, after his lawyers and associates said his condition had dramatically worsened.

In a post on his Instagram account, Mr Navalny described a gruelling search that lasted for several hours before his transfer and wryly described his condition.

“You would laugh if you see me now – a skeleton staggers around his cell,” the post read.

“They can use me to scare children who refuse to eat: ‘If you don’t eat porridge, you will be like that man with big ears, shaven head and hollow eyes’.”

Mr Navalny added a serious note that he was glad to hear from his lawyer about broad sympathy and support for him in Russia and abroad.

His lawyer Vadim Kobzev tweeted that Mr Navalny so far has received only one glucose injection since Sunday at the hospital unit, which is intended to treat tuberculosis patients.

Alexei Navalny’s lawyers Olga Mikhailova, right, and Vadim Kobzev
Alexei Navalny’s lawyers Olga Mikhailova, right, and Vadim Kobzev (Kirill Zarubin/AP)

Six other attempts to give him a shot failed because paramedics apparently were not qualified enough to find his vein, he said.

“His arms are all blue with the shots,” Mr Kobzev said.

Reports about Mr Navalny’s rapidly deteriorating health have drawn international outrage.

His personal doctor Dr Anastasia Vasilyeva led three other medical experts to try to visit Mr Navalny at the prison clinic and the IK-3 prison in the city of Vladimir.

They were denied entry after waiting for hours outside the gates.

“It’s a show of disrespect and mockery of the doctors,” Dr Vasilyeva tweeted, adding that Mr Navalny’s “life and health are clearly in danger”.

Mr Navalny, who is Russian President Vladimir Putin’s most adamant opponent, has been on a hunger strike since March 31 to protest over the prison officials’ refusal to let his doctors visit him and provide adequate treatment for his back pains and numbness in his legs.

Russia’s penitentiary service insists that Mr Navalny was getting all the medical help he needs.

The penal colony where a hospital for convicts is located in Vladimir, a city 180 kilometres (110 miles) east of Moscow, Russia
The penal colony where a hospital for convicts is located in Vladimir, a city 110 miles east of Moscow, Russia (Kirill Zarubin/AP)

The prison service said in a statement on Monday that Mr Navalny’s condition was deemed “satisfactory”.

But another of his doctors, Dr Yaroslav Ashikhmin, said over the weekend that test results provided by his family show Mr Navalny has sharply elevated levels of potassium, which can bring on cardiac arrest, as well as heightened creatinine levels that indicate impaired kidney function.

Mr Navalny was arrested in January upon his return from Germany, where he had spent five months convalescing from a nerve agent poisoning he blames on the Kremlin – an accusation Russian officials have rejected.

His arrest triggered the biggest protests seen across Russia in recent years.

In February, a Moscow court ordered him to serve two-and-a-half years in prison on a 2014 embezzlement conviction that the European Court of Human Rights deemed to be “arbitrary and manifestly unreasonable”.

The penal colony in Vladimir, Russia
The penal colony in Vladimir (Kirill Zarubin/AP)

In response to Mr Navalny’s deteriorating health, his associates have called for a nationwide rally on Wednesday, the same day that Mr Putin is scheduled to deliver his annual state of the nation address.

Russian authorities, meanwhile, have escalated their crackdown on Mr Navalny’s allies and supporters, with the Moscow prosecutor’s office asking a court to brand Mr Navalny’s Foundation for Fighting Corruption and his network of regional offices as extremist organisations.

Human rights activists say such a move would paralyse their activities and expose their members and donors to prison sentences of up to 10 years.