WASHINGTON (NEXSTAR) – Imprisoned Russian opposition leader Alexei Navalny, a vocal critic of President Vladimir Putin, is dead.

Russian authorities say he collapsed and died at the prison where he’s been held for the past several years.

That news is coming from the Russian prison services, but Navalny’s lawyers say they are waiting to confirm that for themselves.

 Alexei Navalny was one of the most well-known antagonists of Russian President Vladimir Putin.

His public crusade against official corruption, along with his massive anti-Kremlin protests, made him a symbol of those fighting against Putin.

He was imprisoned off and on for years by the Russian security services on what were typically considered bogus charges by international observers.

In 2021 Navalny was arrested again after returning to Russia from Germany where he had sought treatment for nerve agent poisoning, he blamed on the Kremlin.

Since then, he’s been transferred between a series of remote Russian penal colonies, serving a 21-year sentence for extremism.

Friday morning, Russian officials announced Navalny fell ill and died but did not provide any other information.

Navalny’s wife, Yulia, speaking Friday at the Munich security conference called for justice in her husband’s death.

Officials are still working to confirm his death independently.

Back in 2021, President Joe Biden warned of “devastating” consequences for Russia if Navalny died in prison.