Russian authorities have threatened to bury Alexei Navalny at the Arctic prison colony where he died if his family does not agree to a closed funeral, the opposition leader's team said Friday.

Navalny, the most vocal critic of President Vladimir Putin, died on February 16 after three years in prison on charges widely seen as retribution for his campaigning against the Kremlin.

Authorities have since refused to hand his body over to his mother, who arrived at the prison colony in northern Siberia last Saturday.

"An hour ago, an investigator 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," Navalny's spokesperson Kira Yarmysh wrote in a post on X.

His mother, Lyudmila Navalnaya, "refused to negotiate... because they have no authority to decide how and where to bury her son", Yarmysh said.

Navalny's team says that Russian officials are "scared" of the opposition leader even after his death and are refusing to allow a public funeral that could become a show of support for his opposition to Putin.

The associates have also called Putin a "killer" who is trying to cover his tracks by not allowing independent forensic analysis of Navalny's body.

Russian police have arrested hundreds of mourners at makeshift memorials to the opposition leader over the last week.

Putin has not publicly commented on Navalny's death.