Jailed Russian opposition leader Alexei Navalny has died, the prison service of the Yamalo-Nenets region where he has been serving his sentence said on Friday.
Mr Navalny, one of the most vocal critics of Russian President Vladimir Putin, had been in prison since February 2021.
Late last year, he was moved to a penal colony in the Arctic Circle.
Russian state news agency TASS reported that Putin had been told of Mr Navalny's death.
In a statement, the Federal Penitentiary Service of the Yamalo-Nenets Autonomous District said Mr Navalny "felt unwell" after a walk on Friday, and "almost immediately lost consciousness".
It said that medical staff had been called, but that they were unable to resuscitate Mr Navalny.
It said the reason of death was being established.
Mr Navalny's press secretary, Kira Yarmysh, posted on X (formerly Twitter) that she had been unable to confirm his death.
She said his lawyer was travelling to the prison where he was being held.
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