In a post on Instagram on Wednesday, jailed Kremlin critic Alexei Navalny announced that he has gone on hunger strike until he receives proper medical treatment for severe back pain and numbness in his legs.

Last week the 44-year-old opposition politician, who is serving a two-and-a-half-year prison sentence in one of Russia's most notorious penal colonies, said he was suffering from a pinched nerve that had caused his right leg to go numb.

In the Instagram post, Navalny said that the back pain that had earlier caused his right leg to go numb was causing his left leg to now lose sensitivity too.

"I have gone on a hunger strike demanding that the law be obeyed and that a visiting doctor be allowed to visit me," he wrote.

Navalny, who is considered a flight risk by authorities, said last week that he is woken eight times per night by guards announcing to a recording camera that he is still in his cell.

On Wednesday, he said that instead of receiving medical treatment he is continuing to be "tortured with sleep deprivation."

Navalny was detained in January after returning to Russia from Germany, where he had been recovering for several months from a poisoning attack he says was orchestrated by the Kremlin.

He was last month sent to prison for 2-and-a-half years on old embezzlement charges his allies and Western governments say are politically motivated.