Russian authorities have threatened to bury Alexei Navalny on the grounds of the prison colony if his family does not agree to hold a private funeral.

The opposition leader’s team said that his mother had been given an “ultimatum” by Russian authorities during a visit to the penal colony where he died.

“An hour ago, investigators called Alexei’s mother and gave her an ultimatum. She has three hours to agree to a secret funeral without a public farewell, or Alexei will be buried in the colony,” Kira Yarmysh, Navalny’s spokesperson, said.

Navalny, 47, fell unconscious and died suddenly last week at the penal colony above the Arctic Circle where he was serving a three-decade sentence, the prison service said.

His 69-year-old mother travelled to the remote IK-3 prison but has reportedly been prevented from seeing his body.

On Tuesday, Lyudmila Navalnaya appealed to Vladimir Putin, the Russian president, for the release of her son’s body.

“I appeal to you, Vladimir Putin. The solution to the issue depends only on you,” she said in a video address.

“Let me finally see my son. I demand that Alexei’s body be released immediately so that I can bury him in a humane way.”

Yulia Navalnaya, Navalny’s widow, released a similar statement, urging authorities to allow him to be “buried with dignity”.

In retaliation for Navany’s death, the US imposed extensive sanctions against Russia on Friday, targeting more than 500 people and entities.

The move was also retribution for the second anniversary of Moscow’s invasion of Ukraine.

President Joe Biden said the measures aim to ensure Putin “pays an even steeper price for his aggression abroad and repression at home”.

Mr Biden, who has directly blamed Putin for Navalny’s death, met the opposition leader’s widow and daughter in California on Thursday and called him “a man of incredible courage”.