Russia’s leading opposition figure has been arrested and detained for 30 days, after returning to Moscow, the country’s capital, for the first time since he was poisoned last year.
Alexei Navalny said a court ruling held inside a police station was a mockery and called for street protests.
Dozens of his supporters gathered outside the Moscow police station where he was being held and shouted “disgrace” and “Putin resign”.
Mr Navalny was held soon after his flight from Germany arrived on Sunday.
Russian prosecutors say he violated the parole terms of a suspended sentence for embezzlement. He said the charges are politically motivated.
Last August, Mr Navalny, 44, was almost killed in a nerve agent attack, which he blamed personally on Russian President, Vladimir Putin.
The Kremlin denies involvement. The opposition politician’s allegations have, however, been backed up by reports from investigative journalists.
On Sunday, big crowds gathered at Moscow’s Vnukovo airport to greet Mr Navalny’s flight from Berlin – but in a last-minute decision the authorities re-routed the plane to another airport in the capital.
A makeshift courtroom was organised on Monday at a police station in Khimki, on the outskirts of Moscow, where Mr Navalny had spent the night.
The judge ordered Mr Navalny’s detention until 15 February for violating his parole. He will have another hearing on 29 January to determine whether his suspended sentence of three-and-a-half years should be replaced with a jail term.
Mr Navalny said his treatment was beyond a “mockery of justice” and described the hearing as “lawlessness of the highest grade”.
“Don’t be afraid. Take to the streets, not for me, but for yourselves, for your future,” he said in a video address (in Russian) from the police station.
A crowd of about 200 Navalny supporters gathered outside the police station in freezing weather, demanding his immediate release.
Mr Navalny was later seen led away by police to one of Moscow’s prisons.
His lawyer, Vadim Kobzev, said they would appeal against the “illegal” court decision, according to Russia’s Interfax news agency.
Russia’s prison service said the opposition leader “had been wanted since 29 December 2020 for repeated violations of the probation period” related to his suspended sentence for embezzlement.
Separately, Russian prosecutors have launched a new criminal case against Mr Navalny on fraud charges related to transfers of money to various charities, including his Anti-Corruption Foundation.
Mr Navalny accuses Mr Putin of targeting him with spurious cases.
Meanwhile, more than 70 Navalny supporters and journalists were detained across Russia on Monday, according to the Monitoring group OVD-Info.