Russian authorities say jailed Russian opposition leader Alexei Navalny has died in prison. He was 47.

Russia's Federal Penitentiary Service of the Yamalo-Nenets Autonomous District in the Arctic Circle said on Friday that Navalny felt unwell after a walk and lost consciousness. It said doctors were unable to resuscitate him, and he was confirmed dead.

Navalny was arrested in 2021 over a past economic incident and imprisoned. Even in prison, he continued criticizing President Vladimir Putin over social media. Following Russia's invasion of Ukraine, he called on people to stage anti-war demonstrations on the streets.

A group supporting the opposition leader said in a social media post in December that he was being held in a prison colony in northern Russia.

Kremlin spokesperson Dmitry Peskov says he thinks doctors will identify the cause of his death.

Human rights groups and Western countries have been seeking Navalny's release. Criticism against the Putin administration is likely to mount following Navalny's death.