Russian opposition leader Alexei Navalny's body is apparently not in the morgue where prison authorities said it was being kept, according to his team.
Mr Navalny's lawyer arrived in the town of Salekhard with Navalny's mother Lyudmila and went to the local morgue.
"It was closed despite the prison saying that it was open and that Navalny's body was there," Navalny's team said on Telegram.
The lawyer called a number for the morgue that he saw on the door and was told that "Alexei's body is not in the morgue", the post said.
Navalny, a 47-year-old former lawyer, fell unconscious and died yesterday after a walk at the "Polar Wolf" Arctic penal colony in Kharp, about 1,900km northeast of Moscow, where he was serving a three-decade sentence, authorities said.
His supporters have called for the body to be returned to the family "immediately".
Navalny's team also said that his mother was told that he had been struck down by "sudden death syndrome" and that his body would not be handed over to the family until an investigation was completed.
"When Alexei's lawyer and mother arrived at the colony this morning, they were told that the cause of Navalny's death was sudden death syndrome," Ivan Zhdanov, who directs Navalny's Anti-Corruption Foundation, said on social media platform X.
"Sudden death syndrome" is a vague term for different cardiac syndromes that cause sudden cardiac arrest and death.
Earlier in a post on X, formally Twitter, a spokeswoman for Navalny, Kira Yarmysh said that Lyudmila Navalnaya had been notified that he died at 2.17pm (9.17am GMT) yesterday and that the body was in Salekhard, a town near the Arctic prison where he was held.
"We demand that Alexei Navalny's body be given to his family immediately," Ms Yarmysh said.
His body was taken to Salekhard by Russian investigators, who were conducting "research", she said.
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Hundreds of flowers and candles laid in Moscow yesterday to honour the memory of Navalny were taken away overnight in black bags.
Yesterday, Russia's prison service said that Navalny fell unconscious and died after a walk at the "Polar Wolf".
Several dozen roses and carnations remained at the monument to the victims of Soviet repression, which sits in the shadow of the former KGB headquarters on Lubyanka Square in central Moscow.
Vladimir Nikitin, 36, was alone laying a carnation at the Solovetsky Stone, which hails from the islands with the same name in the White Sea where one of the first "Gulag" forced labour camps was founded in 1923 by the Bolsheviks.
Policemen looked on.
When asked for an interview by Reuters, Mr Nikitin asked to speak in the underpass which threads beneath Lubyanka Square, citing the fear of detention.
"Navalny's death is terrible: hopes have been smashed," he said.
"Navalny was a very serious man, a brave man and now he is no longer with us. He spoke the truth - and that was very dangerous because some people didn't like the truth."
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At the "Wall of Sorrow" memorial on the avenue named after Soviet physicist and dissent Andrei Sakharov, some Russians laid flowers beside pictures of Navalny. One message read: "We will not forget, nor shall we forgive."
"I came because I have grief," said Arkady, who declined to give his second name. "He was a man who I respected. I had hopes that he was someone who could do something in the future."
The West, including US President Joe Biden, blamed Russian President Vladimir Putin for the death. Western leaders did not cite evidence.
Kremlin spokesman Dmitry Peskov said the reaction of Western leaders to the death was unacceptable and "absolutely rabid".
Russian authorities viewed Navalny and his supporters as extremists with links to the CIA intelligence agency who are seeking to destabilise Russia. They have outlawed his movement, forcing many of his followers to flee abroad.
The death of Navalny, a former lawyer, robs the disparate Russian opposition of its most charismatic and courageous leader as Putin prepares for an election that will keep the former KGB spy in power until at least 2030.
