In a statement on Friday, the Federal Penal Service in Yamalo-Nenets Autonomous Region said that Navalny, 47, who was serving his sentence in a correctional facility on several charges including embezzlement, “felt ill” after going for a walk, losing consciousness almost immediately, Russia Today reported.

Officials said that medics and an ambulance were called without delay. “All the necessary resuscitation measures were carried out, but they did not yield positive results. Paramedics confirmed the death of the convict,” the statement added.

The cause of death is being established. However, according to an RT Russian service source, the oppositon figure had a blood clot.

The Kremlin said that President Vladimir Putin has been informed of Navalny’s death. Spokesman Dmitry Peskov referred questions to the Federal Penitentiary Service, adding that the cause was currently unclear.

Navalny’s lawyer, Leonid Solovyov refused to comment, but explained that his client had held on a meeting on Wednesday. “Everything was normal then,” he insisted.

Navalny was jailed in 2021, over a long-standing fraud case. The previous summer he attracted major international attention after an alleged poisoning in Siberia, which led to a transfer to Germany.