Russian opposition leader Alexei Navalny has "disappeared" from the prison he was being kept in, his team have said.
Navalny's top aide said on Tuesday the 46-year-old had been transferred from the prison where he is serving an 11-and-a-half-year sentence to an undisclosed location.
Navalny's chief of staff Leonid Volkov said his lawyer arrived at Correctional Colony No. 2, around 74 miles east of Moscow, and asked for Navalny, but was told: "There is no such convict here."
"Where Alexei is now, and which colony he is being taken to, we don't know," Volkov said in a statement on Telegram.
Navalny's spokeswoman Kira Yarmysh said there was speculation that he was being taken to the high-security penal colony IK-6 Melekhovo near Vladimir, about 155 miles east of Moscow.
Russia's prison service could not be reached for immediate comment.
"The problem with his transfer to another colony is not only that the high-security colony is much scarier: it is more that we don't know where Alexei is," Yarmysh added.
"He is one-to-one with the system that has already tried to kill him, so our main task now is to locate him as soon as possible".
Navalny, by far Russia's most prominent opposition leader, was poisoned almost two years ago.
Western intelligence claimed he was poisoned with a nerve agent by the Kremlin.
He returned to Russia in January 2021 after recovering from the failed assassination attempt and was immediately arrested when he touched down in Moscow.
Russia initially jailed him for two-and-a-half years for parole violations but in March he had his sentence increased by nine years over allegations of fraud and contempt of court.
The opposition leader says the charges against him are fabricated and aimed at thwarting his political ambitions.
The judge ordered that Navalny be transferred to a maximum-security prison, where his rights to visits and correspondence will be reduced.
Last month, Navalny launched a fresh critique of Vladimir Putin via video link in a Russian court, casting the Kremlin chief as a madman who started a "stupid war" that was butchering the innocent people of both Ukraine and Russia.
Navalny's political network has been largely dismantled since his jailing, having been banned as an "extremist" organisation. Senior aides and organisers have either been jailed or forced into exile.
Navalny said two weeks ago that he had been charged in a new criminal case with creating an extremist organisation and inciting hatred towards the authorities.