Russia’s prison agency announced Friday that prominent Vladimir Putin critic and opposition leader Alexei Navalny has died at the age of 47.

The Federal Penitentiary Service said in a statement that Navalny felt unwell after a walk on Friday and lost consciousness, according to The Associated Press. An ambulance arrived to try to rehabilitate him, but he died, the statement added.

Navalny’s spokesperson said in a post on X that “we have no confirmation of this yet.

“Alexei’s lawyer is currently on his way to Kharp. As soon as we have any information, we will inform him about it,” Kira Yarmysh added.

Alexei Navalny's appearance in court

Russian opposition leader Alexei Navalny appears on a television screen as he appears via video link in a Moscow court on Wednesday, April 26, 2023. (AP/Alexander Zemlianichenko)

Navalny was detained in the IK-3 penal colony, also known as “Polar Wolf”, in Kharp, northern Russia, considered one of the harshest prisons in the country.

Navalny has previously organized anti-government rallies and run as a candidate to advocate for reforms against what he claims is corruption in Russia. He was the victim of an alleged assassination attempt in 2020, when he suffered poisoning from a suspected Novichok nerve agent.

He remained in a coma for several weeks as doctors in Germany struggled to keep him alive. He accused Putin of being responsible for poisoning him.

Navalny then returned to Russia in 2021, when authorities immediately arrested him and later sentenced him to 19 years in prison on extremism charges. His team has repeatedly expressed concern about his treatment after his return and Navalny has said the charges were politically motivated.

Navalny in Moscow, Russia

Russian opposition leader Alexei Navalny looks at photographers at the Babuskinsky district court in Moscow, Russia, in February 2021. (AP Photo/Alexander Zemlianichenko, File) (AP/Alexander Zemlianichenko)

There was no immediate confirmation of Navalny’s death from his team.

The remote region where Navalny was detained is famous for its long, harsh winters. Kharp is about 60 miles from Vorkuta, whose coal mines were part of the Soviet gulag prison camp system.

This is a developing story. Please check for updates.

Michael Dorgan of Fox News and The Associated Press contributed to this report.

By Sam