He was already serving sentences of 11-and-a-half years in a maximum security facility on fraud and other charges he denies.
Supporters of Navalny claim his arrest and incarceration are a politically motivated attempt to stifle his criticism of Russian President Vladimir Putin.
“On Friday and throughout today, neither IK-6 nor IK-7 responded to them,” Yarmysh posted, adding that Navalny had been missing for six days. Navalny was last imprisoned in the IK-6 penal colony east of Moscow.
The White House said it was “deeply concerned” about reports of Navalny’s disappearance.
“He should be released immediately. He should never have been jailed in the first place, and we’re going to work with our embassy in Moscow to see how much more we can find out,” John Kirby, US National Security Council spokesman, told reporters aboard Air Force One.
Navalny was due to appear in court via a video link on Monday, Yarmysh said. Prison authorities told Navalny’s team he was unable to appear for the hearing due to an electricity issue in the prison.
Yarmysh said she was concerned by Navalny’s recent poor health.
“The fact that we cannot find Alexey is especially alarming because last week he became ill in his cell: he became dizzy and laid down on the floor. The colony staff immediately came running, lowered the bed, laid Alexey down and put [him] on an IV,” she said on X.
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“What it was, we don’t know, but given that he was deprived of food, kept in a punishment cell without ventilation and had his walking time reduced to a minimum, it looked like a hungry faint,” Yarmysh said.
The dissident was taken from Russia to Germany in 2020, after he was poisoned with Novichok, a Soviet-era nerve agent. Navalny had to be airlifted from the Siberian city of Omsk and arrived comatose at a hospital in Berlin.
Russia denies involvement in Nalvany’s poising. Putin said in December 2020 that if the Russian security service had wanted to kill Navalny, they “would have finished” the job.
Navalny was immediately incarcerated upon his return to Russia in January 2021, on charges of violating the terms of his probation related to a fraud case brought against him in 2013, which he also dismissed as politically motivated.
He has campaigned from prison against Russia’s invasion of Ukraine and attempted to mobilize public opposition to the war.
“We will conduct an election campaign against the war. And against Putin. Exactly. A long, stubborn, exhausting, but fundamentally important campaign, where we will turn people against the war,” Navalny said, according to a statement on his website.
When Navalny was in August sentenced to 19 years in a maximum security penal colony, he said “the number of years does not matter.”
“I perfectly understand that, like many political prisoners, I am sitting on a life sentence. Where life is measured by the term of my life or the term of life of this regime,” he said in a statement.