Jailed Russian opposition politician Alexei Navalny said on Wednesday that prison authorities had transferred him to a punishment cell for the second time this month at the facility where he is being held on charges he says are trumped up.

Navalny, President Vladimir Putin’s most vocal critic inside Russia, is serving an 11-1/2 year sentence after being found guilty of parole violations and fraud and contempt of court charges. He says all charges against him were fabricated as a pretext to smother dissent and thwart his political ambitions.

In a post on his Twitter and Instagram accounts, each with millions of followers, Navalny wrote via his lawyers that he had been sent to a punishment cell for five days for briefly walking without his hands behind his back in violation of prison rules.

“At this rate, this will become my permanent place of residence,” the 46-year-old said, referring to the cell as a “hellish closet”.

He added: “The directive obviously came from Moscow. Even by the standards of a Russian prison, sending one to the punishment cell just for 3 seconds without hands behind their back is too much.”

The Federal Penitentiary Service did not immediately respond to a request for comment.

Navalny, who was moved in June to a high-security penal colony east of Moscow, said on Aug. 15 that he had been thrown into a punishment cell for failing to button the top button on his prison uniform, which he said was too small for him.

Last year Navalny voluntarily returned to Russia from Germany where he had been treated for what Western laboratory tests showed was a near-fatal attempt to poison him in Siberia with a Soviet-era nerve agent. Russia denies trying to kill him.