Imprisoned Russian opposition leader Alexei Navalny, who has been on hunger strike since March 31, on Friday described threats to force-feed him, using “straitjacket and other pleasures.”

In an Instagram post, Navalny said an official told him that a blood test indicated his health was deteriorating and threatened to force-feed him if he continues to refuse to eat.

“And then she detailed the joys of force-feeding to me. Straitjacket and other pleasures,” the politician said, adding that he urged the officials not to do it, “pointing to a clause in the law.”

Navalny, President Vladimir Putin’s most vociferous critic, is demanding a visit from his physician after developing severe back pain and numbness in his legs in prison.

The 44-year-old opposition leader was arrested in January upon his return from Germany, where he had spent five months recovering from a nerve agent poisoning he blames on the Kremlin — accusations Russian officials have rejected. Navalny’s arrest triggered a massive wave of protests all across Russia, the biggest show of defiance in recent years.

Soon after the arrest, a court ordered Navalny to serve 2 1/2 years in prison on a 2014 embezzlement conviction he said was fabricated and the European Court of Human Rights deemed to be “arbitrary and manifestly unreasonable.” Last month, the politician was transferred to a penal colony east of Moscow, notorious for its harsh conditions.

Also Friday, the Moscow prosecutor’s office said it asked a court to declare Navalny’s Fund for Fighting Corruption as an extremist group and his staff members as extremists.

“The actual goals of their actions are to create conditions for changing the constitutional system, including using the ‘color revolution’ scenario,” Russian news agency Interfax quoted the prosecutor’s office as saying.

Russians broadly use the term “color revolution” to refer to popular uprisings against governments, such as ones that took place in Ukraine and Georgia. Navalny’s arrest set off protests throughout the country in January, the largest show of public dissent in a decade.

Organizers of activities by a group classified as extremist can be prosecuted for crimes that carry prison sentences of up to 10 years, state news agency Tass reported Pavel Chikov, a lawyer for the Agora human rights organization, state news agency, as saying.

Navalny has complained about back pain and said he was losing sensation in his legs. His demands for a doctor’s visit were rebuffed by prison officials, with Russia’s state prison service saying he was getting all the medical help he needed. In response, Navalny went on hunger strike.

The opposition leader charged Friday that prison officials refused to let his physician in because “they fear it’ll transpire that the loss of sensation in the limbs may be connected to the poisoning,” and reiterated he had “an absolutely guaranteed right: to be examined by an independent civilian doctor.”

Describing his state after more than two weeks of a hunger strike, Navalny said his head was “spinning a lot,” but that he was “still walking.”

Navalny’s wife, Yulia, who visited him in prison earlier this week, said the politician was “cheerful” but had trouble talking and lost a lot of weight.

(AP)