The death of Alexei Navalny has been confirmed by his spokesperson, but it remains unclear where the body of the Vladimir Putin critic is.
Spokesperson Kira Yarmysh said in a post on X the most prominent face of the Russian opposition to Mr Putin was "murdered" at a remote Arctic penal colony.
She said Mr Navalny's mother, Lyudmila Navalnaya, was informed by authorities that her son had died on 16 February at 2.17pm, local time.
Russia-Ukraine latest: Follow live updates
Prominent Navalny ally Ivan Zhdanov added that prison officials told Mr Navalny's mother that he had died due to "sudden death syndrome".
But the body of the 47-year-old has not yet been located or released by authorities.
Lyudmila Navalnaya, the mother of late Russian opposition leader Alexei Navalny, and lawyer Vasily Dubkov arrive at the regional department of Russia's Investigative Committee in the town of Salekhard in the Yamal-Nenets Region, Russia February 17, 2024. REUTERS/Maxim Shemetov
Mr Navalny's mother was told by a prison official that her son's body was taken to the nearby city of Salekhard as part of a probe into his death, Ms Yarmysh said.
But when they arrived at the morgue, it was closed, and workers said the body was not there.
Alexey's lawyer and his mother have arrived at the Salekhard morgue. It's closed, however, the colony has assured them it's working and Navalny's body is there. The lawyer called the phone number which was on the door. He was told he was the seventh caller today. Alexey's body is… pic.twitter.com/CsPbONUBrn
— Кира Ярмыш (@Kira_Yarmysh) February 17, 2024
Hours later, Ms Yarmysh said lawyers for the politician were told Mr Navalny's body would not be handed over to his relatives until an investigation into his death had been completed.
She accused the Investigation Committee in Salekhard of "driving us around in circles and covering their tracks" as only hours before they were told the investigation had already been concluded, and nothing criminal had been established.
Photos of Alexei Navalny is seen among flowers and candles at the monument to the victims of soviet occupation in Vilnius, Lithuania, Saturday, Feb. 17, 2024. Poster with the words reading "Putin is a killer", left,. Russian authorities say that Alexei Navalny, the fiercest foe of Russian President Vladimir Putin who crusaded against official corruption and staged massive anti-Kremlin protests, died in prison. He was 47. (AP Photo/Mindaugas Kulbis)
Russia's Federal Penitentiary Service reported on Friday that Mr Navalny felt sick after a walk and became unconscious at the penal colony in the town of Kharp, in the Yamalo-Nenets region, which is within the Arctic Circle.
More than 340 detained in Russia
Meanwhile, more than 340 people have been arrested in Russia since the moment Mr Navalny's death became public, according to independent human rights organisation, OVD-Info.
This included 230 people across multiple cities who were detained on Saturday.
Police detain a man as he wanted to lay flowers paying their last respect to Alexei Navalny at the monument, a large boulder from the Solovetsky islands, where the first camp of the Gulag political prison system was established, in St. Petersburg, Russia on Saturday, Feb. 17, 2024. Russian authorities say that Alexei Navalny, the fiercest foe of Russian President Vladimir Putin who crusaded against official corruption and staged massive anti-Kremlin protests, died in prison. He was 47. (AP Photo
Police officers detain a man during a gathering in memory of Russian opposition leader Alexei Navalny near the Wall of Grief monument to the victims of political repressions in Moscow, Russia February 17, 2024. REUTERS/Stringer TPX IMAGES OF THE DAY
OVD-Info said others had been detained the day before when they came to lay flowers in memory of Mr Navalny.
Read more:
Police in Russia crack down on protests
Russia 'outmatched' by Ukraine's allies
Ukraine's army chief says forces have pulled out of frontline city
Among the arrested included a priest who went to a memorial in St Petersburg to conduct a service in the politician's memory.
A woman lays flowers paying the last respect to Alexei Navalny at the at the monument to the victims of soviet occupation in Vilnius, Lithuania, Saturday, Feb. 17, 2024. Russian authorities say that Alexei Navalny, the fiercest foe of Russian President Vladimir Putin who crusaded against official corruption and staged massive anti-Kremlin protests, died in prison. He was 47. (AP Photo/Mindaugas Kulbis)
In Moscow, social media footage showed a large group of people chanting "shame" as police dragged a screaming woman from the crowd.
Putin 'should be held accountable'
Hours after Mr Navalny's death was reported, his wife, Yulia Navalnaya, made a dramatic appearance at a security conference in Germany where many world leaders had gathered.
She said that she was unsure if she could believe the news from official Russian sources, "but if this is true, I want Putin and everyone around Putin, Putin's friends, his government to know that they will bear responsibility for what they did to our country, to my family and to my husband".
Sir Keir Starmer pays tribute to Alexei Navalny1:06
Play Video - Starmer: 'Navalny was incredibly courageous'
Starmer: 'Navalny was incredibly courageous'
Reacting, Labour leader Sir Keir Starmer said he was "moved" by Mrs Navalnaya's words, adding that Russia has to be held to account.
It came after the UK's Foreign Secretary Lord Cameron said: "We should hold Putin accountable for this. And no one should be in any doubt about the dreadful nature of Putin's regime in Russia after what has just happened."
Foreign ministers of the G7 - made up of Canada, France, Germany, Italy, Japan, the UK and US - have called on Russia to fully clarify the circumstances of Mr Navalny's death.