Putin critic Alexei Navalny, 47, died in an Arctic Circle prison

Alexei Navalny, Russia's most prominent opposition leader of the past decade, has died in an Arctic Circle prison, prisons said.

Navalny, seen as an outspoken critic of President Vladimir Putin, served 19 years in prison on charges considered politically motivated.

Late last year he was transferred to one of Russia's toughest penal colonies.

The prison service in the Yamalo-Nenets district said Navalny was “unwell” after Friday's walk.

He “lost consciousness almost immediately”, it said in a statement, and an emergency medical team was immediately summoned to try to revive him but without success.

“Emergency physicians pronounced the inmate dead. The cause of death is being determined.”

Navalny, 47, was last seen a day ago, smiling and smiling during a court hearing via video link.

Navalny's close aide, Leonid Volkov, wrote in X but declined to comment to Russian media, his lawyer Leonid Solovyov said: “Russian authorities are making confessions that they killed Alexei Navalny in prison. We have no way to confirm or prove that. It's not true.”

Within minutes of Navalny's death being announced by the prison service, the international community praised the courage of Vladimir Putin's greatest domestic enemy.

France said he gave his life to resist Russian “repression”, while Norway's foreign minister said Russian authorities bore the brunt of his death.

Mr Putin's spokesman, Dmitry Peskov, said Navalny's death had been “informed of the president”, who was visiting the city of Chelyabinsk.

Most of the Russian president's critics have left Russia, but Alexei Navalny returned in January 2021 after months of medical treatment. In August 2020, he was poisoned at the end of a trip to Siberia with the Novichok nerve agent.

His crew succeeded in sending him to Germany for special treatment, and upon his return to Moscow he was immediately taken into custody. He will not be out of jail for the next 37 months.

Navalny, 47, has long sought to challenge Vladimir Putin at the ballot box, but he was barred from running in the 2018 presidential election. Next month, Russia's leader will stand without any meaningful opposition.

Anti-war candidate Boris Nadeshtin was barred from standing after thousands of signatures submitted in support of his candidacy were found to be fraudulent.

Navalny, who launched his protest in the form of an anti-corruption campaign, is the latest in a string of prominent Russian figures to die challenging Vladimir Putin's rule.

Opposition leader Boris Nemtsov was shot dead on a Moscow bridge a stone's throw from the Kremlin in 2015, and Wagner boss Yevgeny Prigozhin was killed in an unexplained plane crash in August 2023, just weeks after leading his mercenaries in an armed revolt.

However, Navalny has repeatedly laughed off his friends' concerns about his health. He was transferred from a penal colony east of Moscow in December and was not seen for several weeks until he reappeared in a penal colony in the Arctic city of Karp.

Navalny, who has been taken on a 20-day tour of Russia, told reporters during a video court appearance that his conditions were “much better” than his previous penal colony in Vladimir.

However, he was repeatedly sentenced to solitary confinement by his jailers. As of last month, he had been single for more than 280 days, his spokeswoman Kira Yarmish said.

Navalny didn't leave prison until he was 70 because of his most recent conviction for terrorism last August. It was his third prison sentence and supporters accused the Kremlin of trying to silence him for good.

Russian human rights activist and journalist Eva Merkacheva said Friday that she had been held in solitary confinement at least 27 times and that it could not have played a role in her death.

He said that doctors knew that under such harsh conditions, such punishment was very harmful to the human body, so under the law no one could be kept in isolation for more than 15 days.