The mother of Alexei Navalny accused Russian officials of pressuring her into a "secret" burial for her son and said she would not agree to it.

"They are blackmailing me, they put conditions for where, when and how Alexei should be buried. This is illegal," Lyudmila Navalnaya said in a video published by his team.

"They want it to be done in secret, with no farewell."

"They want to bring me to the edge of a cemetery, to a fresh grave and say: here lies your son. I don't agree to this," Navalnaya said in a YouTube video.

There was no immediate response from Russian investigators.

Navalny, 47, Russia's best known opposition politician, died suddenly in an Arctic penal colony last week. His team and family have alleged that the Kremlin murdered him, an allegation the Kremlin has angrily rejected.

His mother on Thursday said she had been shown his body and death certificate.

Navalny's team said the death certificate stated that the opposition politician had died of natural causes.

Foreign Minister Sergei Lavrov on Thursday called the West's reaction to Navalny's death "hysteria," and said that Western countries had no right to meddle in Russia's affairs.