A court in Russia has extended Alexei Navalny’s prison sentence by 19 years, and sentenced him to a special regime with the harshest prison conditions in the country. Navalny, 47, once led street protests against the Russian president, Vladimir Putin, built a nationwide political opposition, and revealed salacious details of Kremlin officials’ corrupt lifestyles. As revenge, Russia has sentenced him to a cumulative three decades in prison, a term that will most likely keep the Kremlin critic behind bars and out of politics for as long as Putin remains alive. Navalny attended the sentencing, which was handed down on Friday in a closed hearing inside a penal colony auditorium, in a black prison jumpsuit. Journalists and members of the public have been barred from attending the trial. He was found guilty on six counts, including inciting and financing extremism, creating an illegal NGO, the rehabilitation of Nazism, and inciting children to dangerous acts. He and his supporters have rejected the charges as being politically motivated. Judge Andrey Suvorov said he had delivered a “definitive penalty” against Navalny, whom he described as a “recidivist” in the ruling. The verdict sentenced Navalny to a special prison regime that will limit his ability to meet visitors or write or receive letters for years after his term begins. The conditions will further limit his ability to direct the opposition movement that he founded in Russia and that he has continued to try to manage from behind bars since being jailed in 2021. “They are going to make it almost impossible for him to communicate with the outside world and to have an impact on the outside world,” said Yevgenia Albats, an independent Russian journalist who communicated regularly with Navalny. “They are trying to silence him. To make him dead for the outside world.” Daniel Kholodny, a TV technician working for Navalny’s YouTube channel, stood trial alongside him and was found guilty of organising an extremist group. His lawyer told the independent Novaya Gazeta newspaper that Kholodny was sentenced to eight years in prison. Navalny was already serving an 11-and-a-half year sentence for fraud and other charges that he has described as spurious. His supporters have been tracked down and arrested for supporting his “extremist” movement. After Friday’s verdict, Navalny said that the official length of the sentence was not important. “I perfectly understand that, like many political prisoners, I am sitting on a life sentence. Where life is measured by the term of my life or the term of life of this regime,” he said in a message passed to his lawyers and posted online. In the message, Navalny called on Russians to resist the Kremlin, saying the purpose of the new prison sentence was “to intimidate you, not me”. Since Russia’s full-scale invasion of Ukraine began, judges have begun handing down extremely long prison sentences to Putin’s critics and others accused of betraying their country. Vladimir Kara-Murza, another Russian opposition critic, was recently sentenced to 25 years in prison for treason and other charges tied to his criticism of the Russian invasion of Ukraine. Navalny said: “We know for sure that if one in 10 of those outraged by the corruption of Putin and his officials took to the streets, the government would fall tomorrow. We know for sure that if those who are against the war took to the streets, they would stop it immediately.” His trial was held behind closed doors at the IK-6 penal colony in Melekhovo, about 145 miles (235km) east of Moscow. The opposition leader appeared thin but defiant in his first appearance on a closed circuit television feed. But a judge quickly closed the trial to the public, limiting publicity and making it nearly impossible to follow the proceedings. State prosecutors had requested that Navalny get a further 20 years on the six criminal charges. In a closing statement at his trial, Navalny said: “For a new, free, rich country to be born, it must have parents. Those who want it, who expect it and who are willing to make sacrifices for its birth.” The special prison sentence will include other harsh measures. Navalny can only see family once a year and receive one parcel each year. He will be forbidden from talking to fellow inmates. Convicts are led around the prison with their heads bent down and are only allowed to take occasional walks inside a closed courtyard. Albats said: “Putin is giving him a message (and make no mistake, it is Putin): ‘You were publishing about my palace, my wife, my lovers. Now you get the message back.’ It’s a revenge from Putin for sure.” Putin, 70, is widely expected to assume another six-year term as president beginning in 2024, meaning he could remain in power until 2030 or even 2036, according to new constitutional rules. His time in power, which began in 1999, could potentially surpass that of even Joseph Stalin, who ruled the Soviet Union for almost 31 years. Russia has become far more repressive since it invaded Ukraine, with most of the country’s high-profile opposition people either in prison or forced into exile. Navalny, however, was always a special target. He was arrested in early 2021 after recovering from an attempted assassination by poison that has been tied to the FSB security service. First sent back to prison for violating an old probationary term, he was then given a further nine years for fraud and contempt of court. He is also facing terrorism charges that could add decades more to his prison sentence. In February, Putin ordered the FSB to raise its game and said it was necessary “to identify and stop the illegal activities of those who are trying to divide and weaken our society”.