Lyudmila Navalnaya, the mother of dead Russian opposition leader Alexei Navalny, demanded on Tuesday that President Vladimir Putin hand over her son's body so she could bury him.

Navalny, 47, fell unconscious and died suddenly on Friday after a walk at the "Polar Wolf" penal colony above the Arctic Circle where he was serving a three-decade sentence, the prison service said.

Speaking in a video filmed in front of the prison as small snowflakes swirled in the air, his mother - dressed in black - complained she did not even know where her son's corpse was and demanded Putin give the order to release it.

"For a fifth day, I cannot see him; they aren't giving me his body and don't even tell me where he is," Navalnaya said in the message, which was broadcast on the Navalny LIVE YouTube channel.

"I appeal to you, Vladimir Putin. Resolving this issue depends on you alone. Let me finally see my son.

"I demand that Alexei's body be released immediately so that I can bury him humanely."

She also sent an official letter to Putin with the same demand.

Navalny's allies have cited a Russian investigator as saying that the authorities need at least 14 days to conduct various chemical tests on his body and can not, therefore, hand his corpse over yet.

The West and Navalny's supporters say Putin is responsible for Navalny's death. The Kremlin has denied involvement and said that Western claims that Putin was responsible were unacceptable.

Putin has made no public comment on Navalny's death, but it has further deepened a gaping schism in relations between Moscow and the West caused by the nearly two-year Ukraine war.