The prominent critic of Vladimir Putin, Alexei Navalny, has reportedly died in a harsh Siberian prison, with Kremlin adversaries asserting that he was murdered.

Officials from the prison announced today that the 47-year-old Russian opposition leader collapsed inside the Polar Wolf jail, where he was incarcerated, and efforts to resuscitate him were unsuccessful.

Navalny, a formidable opponent of Putin and a leading domestic critic in Russia, fearlessly challenged the tyrant’s aggressive actions in Ukraine.

Facing severe health issues during his imprisonment, Navalny, as per prison authorities, collapsed mysteriously while taking a walk in the prison compound.

Russian personnel claimed that medical assistance was summoned, but they were unable to revive him, the U.S. Sun is reporting.

Conflicting reports suggest that the Kremlin critic may have been in solitary confinement when the reported incident occurred, as indicated by the Human Rights Foundation.

Strong critics of Putin have already condemned the Russian leader, labeling Navalny’s alleged death as “political murder.”

Written by B.C. Begley