Jailed Russian opposition leader and President Vladimir Putin critic Alexei Navalny, 47, has died in prison, the Office of the Federal Penitentiary Service of Russia said in a statement on Friday, per reports by multiple news outlets.
“On Feb. 16, 2024, in correctional colony No 3, convict A A Navalny felt unwell after a walk, almost immediately losing consciousness,” Sky News’ English translation of the Russian statement read.
“The institution’s medical workers immediately arrived and an emergency medical team was called. All necessary resuscitation measures were carried out, but they did not yield positive results. Emergency medical doctors confirmed the death of the convict.”
TIME has reached out to the Russian government for further information.
In a post shared on X (formerly Twitter), Navalny’s chief of staff, Leonid Volkov, said that his team had no way to confirm whether the reports from federal prison officials were true. Volkov added that Navalny’s lawyer is on the way to Harp [Kharp, a town in Russia] to investigate.
Navalny previously survived what he said was an attempt on his life from nerve agent poisoning that he blamed on the Russian government. Russia, at the time, denied he was poisoned.
Navalny was arrested upon re-entering Russia after recovering in Germany and has been in prison since 2021. He was serving a total sentence of 30 years on charges of extremism. In 2023, he disappeared for three weeks, prompting fears for his physical safety, only to be discovered in a penal colony above the Arctic Circle.
Following the reports of Navalny’s death, the Investigative Committee of the Russian Federation posted on its Telegram channel that it has organized a procedural investigation into the matter.
The Russian Ministry of Foreign Affairs posted a quote from spokesperson Maria Zakharova on X: “The instant reaction of NATO leaders to the news of Alexey Navalny’s demise in the form of direct accusations vs. Russia is self-exposing. No forensic medical examination data IS available, yet the West has already voiced its ‘conclusions.’”
Meanwhile, world leaders have spoken out. U.K. Prime Minister Rishi Sunak said in a post on X: “This is terrible news. As the fiercest advocate for Russian democracy, Alexei Navalny demonstrated incredible courage throughout his life. My thoughts are with his wife and the people of Russia, for whom this is a huge tragedy.”
In 2011, Navalny founded the Anti-Corruption Foundation to investigate corruption among government officials. Russia classified it as an extremist organization in 2021. Navalny participated in mass protests against the government in 2011, after which he was arrested and jailed. He continued his anti-corruption campaigning and made an unsuccessful bid to be the Mayor of Moscow in 2013.
In letters written to TIME from prison, published in Jan. 2022, Navalny said that he wanted the U.S. to pressure the Kremlin from without, as he and others did from within, with the goal of creating a free, democratic Russia at peace with its neighbors and the West.
Navalny had also spoken out against Russia’s invasion of Ukraine.
“I am proud to be my father’s daughter and walk tall knowing that despite the inhuman conditions, he has been standing up against Putin’s war in Ukraine and calling on the Russian people to do everything in their power to fight it,” his daughter Dasha (Daria) Navalnaya wrote for TIME in 2022.