Warsaw, Poland– Yulia Navalnaya, the widow of late Russian opposition leader Alexei Navalny, accused President Vladimir Putin of "satanism" on Saturday for not allowing the body to be returned to his family.

Navalny's mother Lyudmila has said authorities are threatening to bury him on the grounds of the Arctic prison colony where he died earlier this month if she did not agree to a "secret" funeral.

"You tortured him alive, now you torture him while he is dead," Yulia Navalnaya, who has vowed to continue her husband's work, said in a new video, published Saturday.

Russian authorities have said only that an investigation is ongoing and have previously criticised accusations from Navalnya as "unfounded and vulgar".

Navalnaya said on Saturday she believed the pressure being put on Navalny's mother was coming directly from Putin.

"Putin is directing it all. It's Putin saying, 'Put pressure on the mother, break her, tell her the body of her son is rotting'," she said.

"This is the same Putin that likes to show that he is a practising Christian," she said.

Putin has for decades portrayed himself as a devoted Orthodox Christian and has in recent years focused on promoting what he calls "traditional values."

"What Putin is doing now is hatred. No, not even hatred, it's some kind of satanism," Navalnaya said.

"We always knew that Putin's faith is fake, but now we can see it like never before," she added.

On the anniversary of Russia launching its military offensive, the late Kremlin critic's wife also denounced Putin's decision to send troops into Ukraine.

"You will answer for all of this... And for this (Navalny's death) and for the war that you unleashed two years ago, also hiding behind Christian values," Navalnaya said.

"You are just killing. You are just killing sleeping people at night with missiles blessed by the church."