Russian opposition leader Alexei Navalny, who had been serving his sentence in the Yamalo-Nenets region, has died, according to the prison service of the region. He was 47.

The Federal Penitentiary Service of the Yamalo-Nenets Autonomous District stated that Navalny became unwell after a walk on Friday and soon lost consciousness. Medical personnel were called to attend to him but were unable to revive him. The cause of death is currently under investigation.