The Russian penitentiary service said on Friday that opposition figure Alexey Navalny died in a prison colony where he was serving his sentence.

The service said in a statement that Navalny lost consciousness after a walk in the Arctic Yamalo-Nenets Autonomous District, where the colony is located.

The ward immediately called for an ambulance, and all the necessary resuscitation measures were taken but to no avail, according to the release.

"The doctors of the emergency medical service pronounced the convict dead," the prison service said.

Kremlin spokesman Dmitry Peskov said the doctors should determine the cause of Navalny's death.

"The Federal Penitentiary Service is now taking the steps that need to be taken in such a situation according to the rules that exist. I have nothing more to say," he noted.

The Russian daily Kommersant, quoting Peskov, said Russian President Vladimir Putin was informed about the politician's death.

In a separate statement, the Russian Federal Penitentiary Service said it is sending an inspection to the colony to find out all the circumstances of the politician's death.

For its part, the Russian Investigative Committee announced that it would carry out its own investigation of all circumstances of Navalny's death.

Russian Foreign Ministry spokeswoman Maria Zakharova, for her part, said "the immediate reaction of NATO leaders to Navalny's death in the form of direct accusations against Russia is self-revealing."

"There is no forensic examination yet, but the conclusions of the West are already ready," she wrote on Telegram.

Navalny was arrested in January 2021 after a hospital stay in Germany, where he was being treated for poisoning. Western countries and Navalny himself blamed Russia for the poisoning, a claim the Kremlin denies.

In August, he was handed a 19-year prison sentence on charges of extremism, and other crimes. He was already serving an 11.5-year sentence on fraud charges.