Aleksei Navalny, the Kremlin's biggest foe and Russia's most prominent political prisoner, marks his 47th birthday on June 4 in solitary confinement in prison, as supporters held rallies and individual protests to highlight his plight, leading to dozens of arrests and detentions.
Navalny is serving sentences that add up to 11 1/2 years for violating the terms of a parole, contempt of court, and embezzlement through fraud that he and his supporters have repeatedly rejected as politically motivated and designed to silence him.
He is currently in a punitive solitary confinement at a prison in the Vladimir region east of Moscow.
"As always, on my birthday, I want to thank all the people I've met in my life. The good ones for having helped and still helping me. The bad ones for the fact that my experience with them has taught me something. Thanks to my family for always being there for me!" Navalny wrote on Twitter.
"But the biggest thank you and biggest salute I want to give today goes to all political prisoners in Russia, Belarus, and other countries. Most of them ...have it much harder than me. I think about them all the time. Their resilience inspires me every day," he added.
Risking their own detention amid President Vladimir Putin's crackdown on any dissent, supporters held individual pickets in Moscow, St. Petersburg, and elsewhere in the country.
A heavy security presence was seen in central Moscow, with National Guard troops stationed near Pushkin Square.
According to OVD-Info, an independent human rights defense and media group, several people were detained in the capital for holding signs in support of the activist, including a woman identified as Yekaterina Lubyanaya, who was holding a balloon with "Happy birthday!" written on it.
OVD-Info said that more than 100 people had been detained in 23 cities at rallies and individual pickets by late on June 4. At least four detainees were minors and one journalist was held, it said, adding that some were eventually released from custody.
Demonstrations were also reported in several European cities and in Japan and Australia.
A demonstration in support of Aleksei Navalny in St. Petersburg is stopped by police on June 4.
Navalny has been in prison since February 2021 following his arrest one month earlier after he returned from Germany, where he was treated for a near-fatal poisoning that he blamed on the Kremlin, which has denied any involvement.
He and his team have said the charges against him are trumped up for his efforts to expose corruption in the Russian government.
WATCH: Russia's most famous political prisoner spends most of his time in a 2.5-by-3-meter isolation cell. Supporters of Aleksei Navalny have created a traveling exhibition complete with a mock-up of the cell.
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In Jail With Navalny: Mock-Up Shows Conditions In Russian Prison
A Moscow court has set a June 6 date for a hearing for a new trial for Navalny on a charge of extremism, which could keep him in prison for 30 years. He also said an investigator told him that he would also face a separate military court trial on terrorism charges that potentially carry a life sentence.
On June 2, Navalny released excerpts of his correspondence with prison administrators detailing sarcastic demands for outlandish things such as a bottle of moonshine and a pet kangaroo.
Prison officials denied all of his requests, according to the correspondence, often in stilted, bureaucratic Russian.
"When you are sitting in a punishment isolation cell and have little entertainment, you can have fun with correspondence with the administration," Navalny said on Twitter in a series of tweets posted on June 2, apparently by his team.
Among the items he requested was a megaphone to be given to the prisoner in a nearby cell "so he can yell even louder." Another was a request for an inmate who "killed a man with his bare hands" to be awarded with the highest rank in karate.
"The question of awarding eastern martial-arts qualifications is not handled by the administration," the prison wrote back on April 28.
Prison officials also turned down requests for moonshine, tobacco for rolling cigarettes, a balalaika, and the kangaroo.
In response to his wish for a pet kangaroo, the prison wrote: "The animal identified in your request relates to the double-crested marsupial.... Your request is left without satisfaction."
In mock outrage over the refusal, Navalny said he would continue to fight for his "inalienable right to own a kangaroo." The politician said inmates can have a pet if the prison administration allows it.