Russian opposition politician Alexei Navalny has died in prison, according to Russian authorities.

The ardent critic of President Vladimir Putin has been jailed since 2021.

In December, he was moved to an artic penal colony, thousands of miles to the northeast of Moscow in Siberia.

A reason has not yet been given for his death, though prison authorities have said he felt unwell after a walk on Friday and then fell unconscious.

Putin has been informed of Navalny's death, according to Kremlin spokesman, Dmitry Peskov.

Peskov also said that Russia's penitentiary service was making "all checks" regarding Navalny's death but that he had no other information about the matter.