The mother of deceased Russian opposition leader Alexei Navalny says the authorities have shown her his body, but refused to hand it over and pressured her to bury him in secret.

The revelations were included in a video released by Lyudmila Navalnaya on Thursday. The Russian authorities said on Friday last week that Navalny had died in a prison where he was being held.

Navalny's mother said the authorities took her to see his body at a morgue on Wednesday evening. She said they tried to blackmail her and set conditions on where, when and how he should be buried.

She said the officials threatened to do something to the body if she did not agree to a secret funeral. She quoted one of them as saying time was not on her side as the corpse was decomposing.

Navalny's mother says she recorded the video as the authorities began threatening her. She continued to demand that the body be transferred to her immediately.

Navalny's mother and his support group said the officials made her sign a death certificate stating he had died of natural causes.

This comes as the Kremlin is widely alleged to have had a hand in Navalny's death.