Western leaders have held Vladimir Putin directly responsible for the death of the Russian opposition leader Alexei Navalny, as the US president, Joe Biden, called it “yet more proof of Putin’s brutality”. Navalny, 47, died while being held in a jail about 40 miles north of the Arctic Circle, where he had been sentenced to 19 years under a “special regime”. “Make no mistake, Putin is responsible for Navalny’s death,” Biden said in remarks from the White House on Friday. The death of Navalny, once Putin’s most significant political challenger, is a watershed moment for Russia’s shattered pro-democracy movement, which has largely been jailed or driven into exile since the Ukraine invasion of 2022. Though Navalny and his many supporters expected he could die behind bars, few thought it would be so soon. Reports of his death sent a shockwave of anger and disbelief through the ranks of his supporters, including his family. “I don’t know whether to believe the terrible news,” his wife, Yulia, said during a speech at the Munich Security Conference. “But if it is true, then I would like Putin, his staff, his friends, his government, to know that they will be punished for what they’ve done with our country, my family and my husband. They will be brought to justice, and that day will come very soon.” Navalny’s death raises questions about what tools the west still has to constrain or punish Putin, who has faced sanctions since 2022 and has been indicted by the international criminal court for the abduction of Ukrainian children. Biden in 2021 promised “devastating” consequences for Russia if Navalny were to die behind bars. However, it is not clear what could restrain Putin from a further crackdown on Navalny’s supporters in Russia and abroad. In his remarks, Biden praised Navalny’s courage and his decision to return to Russia despite facing near-certain imprisonment. “He bravely stood up to the corruption, the violence and all the bad things that the Putin government was doing,” Biden said. “In response, Putin had him poisoned, he had him arrested, he had him prosecuted for fabricated crimes, he sentenced him to prison, he held him in isolation … Even in prison he was a powerful voice for the truth.” Russia has claimed Navalny died of natural causes. In a statement, the federal penitentiary service for the region where Navalny was incarcerated said he “felt unwell after a walk and almost immediately lost consciousness”. “All necessary resuscitation measures were carried out but did not yield positive results,” the statement said. “The paramedics confirmed the death of the convict.” The Kremlin said Putin had been informed but had no further information. Western reaction was swift, as top officials from the US and Europe accused the Kremlin of causing Navalny’s death. The Foreign Office summoned the Russian embassy in London, adding “we hold the Russian authorities fully responsible.” The US secretary of state, Antony Blinken, said: “His death in a Russian prison and the fixation and fear of one man only underscores the weakness and rot at the heart of the system that Putin has built. Russia is responsible for this.” Putin’s press secretary, Dmitry Peskov, responded angrily, calling western leaders’ remarks “absolutely outrageous and absolutely unacceptable”. In Moscow and St Petersburg, small groups of Russians braved strict anti-protest laws and laid flowers at makeshift memorials to Navalny. At least one person was detained for holding up a placard that appeared to say “murderers” according to footage on social media. Navalny had looked healthy when he appeared by video for a courtroom appeal on Thursday. Speaking from prison, he had complained about the frequent fines he had received while in a punitive cell and asked the judge to send him some money “as my own is running out thanks to your decisions”. The cause of death had not been established, the penitentiary service said. Last year Navalny was treated in hospital after complaining of malnourishment and other ailments caused by mistreatment in prison. Navalny is survived by Yulia and their two children. On 14 February, his team published an Instagram post dedicated to his wife in which he wrote: “I feel that you are close to me every second and I love you more and more.” Navalny was last seen by his lawyer on Wednesday, who said “everything was normal then”. Leonid Volkov, another close ally, said: “We have no reason to believe the state propaganda … If this is true, then it’s not ‘Navalny died’, but ‘Putin killed Navalny’ and that’s the only way [to report it]. But I don’t believe them [for a second].” In early December, Navalny disappeared from a prison in the Vladimir region, where he was serving a 30-year sentence on extremism and fraud charges that he had called political retribution for leading the anti-Kremlin opposition of the 2010s. He did not expect to be released during Putin’s lifetime. Supporters and allies were visibly stunned by the news of his death, and many pointed the finger directly at the Kremlin. Dmitri Muratov, the editor of Novaya Gazeta, told Reuters that Navalny’s death was “murder” brought on by his mistreatment in prison. Mikhail Fishman, a journalist, blinked back tears on the TV Rain channel as he said: “We must learn to live with this news somehow. But we understand the scale of what has happened, that we will mark this as a before-and-after moment.” The US national security adviser, Jake Sullivan, told National Public Radio: “If it’s confirmed, it is a terrible tragedy.” Several other foreign officials also said Putin was directly responsible. “Alexei Navalny fought for the values of freedom and democracy. For his ideals, he made the ultimate sacrifice,” the European Council president, Charles Michel, posted on X. “The EU holds the Russian regime for sole responsible for this tragic death.” Ukraine’s president, Volodymyr Zelenskiy, said it was “obvious” that Putin was behind Navalny’s death. The German finance minister, Christian Lindner, said: “Alexei Navalny fought for a democratic Russia. For that, Putin tortured him to death.” Navalny, a former nationalist politician, helped foment the 2011-12 protests in Russia by campaigning against election fraud and government corruption, investigating Putin’s inner circle and sharing the findings in slick videos that garnered hundreds of millions of views. The high-water mark in his political career came in 2013, when he won 27% of the vote in a Moscow mayoral contest that few believed was free or fair. He remained a thorn in the side of the Kremlin for years, identifying a palace built on the Black Sea for Putin’s personal use, mansions and yachts used by the ex-president Dmitry Medvedev, and a sex worker who linked a top foreign policy official with a well-known oligarch. “He changed what it meant to be a politician in Russia when there was more freedom,” said Ben Noble, an associate professor of Russian politics at University College London and a co-author of Navalny: Putin’s Nemesis, Russia’s Future? “His ability to use social media effectively to reach new audiences, to act as an anti-corruption activist, protest leader, and opposition politician – he was quite extraordinary in this breadth of work. The activation of younger people also led to hope, that politics was something that they could get involved in.” In 2020, Navalny fell into a coma after a suspected poisoning using novichok by Russia’s FSB security service and was evacuated to Germany for treatment. He recovered and returned to Russia in January 2021, where he was arrested on a parole violation charge and received the first of several jail sentences that would have amounted to more than 30 years behind bars. “Navalny left one Russia, returned to another, and perished in a third, where political prospects are absent in principle,” wrote Alexander Baunov, a senior fellow at the Carnegie Russia Eurasia Center. “There are only martyrs.” Putin has recently launched a presidential campaign for his fifth term in office. He is already the longest-serving Russian leader since Joseph Stalin and could surpass him if he runs again for office in 2030, a possibility since he had the constitutional rules on term limits rewritten in 2020. “Alexei Navalny will not be forgotten,” said Andrei Kolesnikov, another senior fellow at the Carnegie Russia Eurasia Center. “He was an absolutely unique example of a fearless politician in a country where politics in the traditional sense of the word was directly prohibited, under threat of repression. In a normal political competition, he would have had a chance to become the head of state.”