Alexei Navalny's allies accuse Russian authorities of deliberately withholding his body

Allies of Russian opposition leader Alexei Navalny are demanding that Russian authorities release his body to his mother and lawyer, claiming it is being deliberately withheld. Russian authorities announced Navalny died in an Arctic prison camp on Friday.

The complaint came as hundreds of Russians paying their respects to the vocal critic of Russian President Vladimir Putin at memorials across the country were detained by authorities, according to human rights observers.

After expressing skepticism over whether he died, Navalny's team confirmed his death, alleging the 47-year-old was murdered and that Russian investigative authorities took away his body for further examination, according to Kira Yarmysh, Navalny's spokesperson.

Navalny's team claimed that Russian authorities are deliberately withholding his body from his family and lawyer, expressing concern that authorities could be trying to cover up signs of how he died if he was murdered.

Yarmysh said local investigative police have indicated Navalny's body won't be handed over until after a new "examination" is completed next week.

Navalny's team also claimed that his body is not in the morgue in Salekhard -- the town near to the prison colony where he died -- despite officials telling them so.

Another of Navalny's associates, Ivan Zhdanov, suggested that the body has not been released as the cause of death has not been established.

"When Alexey's lawyer and mother arrived at the colony this morning, they were told that the cause of Navalny's death was sudden death syndrome," Zhdanov said in a statement.

Navalny's team said they were told that a histological examination was performed on his body.

"The results will supposedly be available next week. It's obvious that they are lying and doing everything they can to avoid handing over the body," his team said in a statement.

Navalny's death drew response from around the world, with world leaders sharing their condolences and U.S. officials blaming his death on Putin.

President Joe Biden issued remarks on Friday, saying he was both "not surprised and outraged" while placing the blame directly on Putin and his allies. Asked whether the U.S. is considering imposing more sanctions against Russia, Biden told reporters that the U.S. is looking at a number of options.

Russian Foreign Ministry spokeswoman Maria Zakharova pushed back Friday against the reaction from NATO leaders to Navalny's death, calling the accusations against Russia "self-exposing" and saying there hasn't been a forensic examination yet, but the West's conclusions were already ready.

Kremlin spokesman Dmitry Peskov also denounced the blame from Western countries.

"The statements of Western countries are completely obvious," Peskov said. "There is no statement from doctors, no information from forensic experts, no final information from the Federal Penitentiary Service, no information about the causes of death. And there are such statements. It is obvious that they are absolutely rabid. We consider such statements absolutely unacceptable."

Meanwhile, at least 401 people have been arrested in 32 Russian cities as people try to leave flowers at sites to pay their respects to Navalny on Friday and Saturday, according to OVD-Info, an independent Russian human rights media project aimed at combating political persecution. Police in riot gear were seen in video footage detaining some and threatening to disperse people.  

In Moscow, dozens of police were posted by the monument to Victims of Political Repression, which honors victims of the Soviet-era police state, according to videos circulating. The videos show dozens of police officers appearing to roughly detain people and dragging some into police vans. In St. Petersburg, photos show police in full riot gear on guard at a similar monument where people have brought flowers.

Thousands of Russians also gathered in cities elsewhere around the world, including London, to protest Navalny's death on Friday night.

ABC News' Natalia Shumskaia contributed to this report