Russian opposition leader Alexei Navalny decried a "mockery of justice" as he faced a hearing at a makeshift court in a police station where a judge ordered he be jailed until February 15.
The hearing comes a day after he was arrested on returning to Moscow for the first time since he was poisoned in the summer of 2020.
The anti-corruption campaigner urged his supporters to "not be silent" and "resist". "Take to the streets not for me, but for you," Mr Navalny said.
In a video released by his team at the hearing, Mr Navalny said the authorities had “have ripped up and thrown away” Russia’s criminal code.
"This is impossible. It's ultimate lawlessness,” he said.
Russian officials said he was detained moments after his arrival in Moscow for multiple breaches of a 2014 suspended sentence for fraud.
Western leaders and human rights groups condemned Mr Navalny’s arrest and called for his immediate release.
However, Russia’s Foreign Minister Sergei Lavrov accused western politicians of seeking to divert attention from their own problems and what he described as “the deepest crisis the liberal development model has found itself in”.
The European Union called for Mr Navalny's immediate release.
"The EU will follow closely the developments in this field and will continue to take this into account when shaping its policy towards Russia," said Josep Borrell, the bloc's foreign policy chief.
Germany’s Foreign Minister Heiko Maas said the detention of Mr Navalny was “totally incomprehensible” and that Russia “is bound by its own constitution and by international obligations to the principle of the rule of law and to the protection of civil rights”.
“These principles must, of course, be applied to Alexei Navalny as well. He should be released immediately,” Mr Maas said on Monday.
Britain’s Foreign Secretary Dominic Raab also called for his immediate release.
“It is appalling that Alexey Navalny, the victim of a despicable crime, has been detained by Russian authorities,” Mr Raab said. “Rather than persecuting Mr Navalny, Russia should explain how a chemical weapon came to be used on Russian soil."
British minister Nadhim Zahawi said the UK was concerned about the safety Mr Navalny.
“We have to make sure that the Russian government answers why a poison was used against Alexei Navalny,” Mr Zahawi told Sky News on Monday.
The arch-critic of the Kremlin fell seriously ill during a flight over Russia in August and was flown to Germany in an induced coma. Western experts said he was poisoned with the Russia-designed nerve toxin Novichok. Moscow denies the accusations.
Mr Navalny was being held by police "illegally" and denied access to a lawyer, his foundation said on Monday.
"Navalny is a Russian citizen. He was illegally detained. Lawyers are not allowed to see him," his Anti-Corruption Foundation said.
The condemnation of his arrest follows that by US, Canadian and other EU officials on Sunday.
European Council president Charles Michel said Mr Navalny's arrest was "unacceptable", while France said his detention caused "great concern".
“With its European partners, [France] is following the situation with the utmost vigilance and calls for his immediate release,” said the French foreign ministry.
US Secretary of State Mike Pompeo said the “detention is the latest in a series of attempts to silence Navalny and other opposition figures and independent voices who are critical of Russian authorities”.
Jake Sullivan, the national security adviser for US president-elect Joe Biden, said the detention was "not just a violation of human rights, but an affront to the Russian people who want their voices heard".
"Mr Navalny should be immediately released, and the perpetrators of the outrageous attack on his life must be held accountable," Mr Sullivan said.
The prison service issued a warrant for Mr Navalny’s arrest last week, saying he had breached the terms of a suspended sentence handed in 2014 on charges of embezzlement.
It has also asked a Moscow court to return Mr Navalny’s to custody to serve his three-and-a-half-year term.
After boarding the flight for Moscow in Berlin on Sunday, Mr Navalny said of the prospect of arrest: “It’s impossible. I’m an innocent man.”
Mr Navalny's supporters went to Moscow’s Vnukovo Airport, where the plane was scheduled to land, but it ended up touching down at Sheremetyevo airport, about 40 kilometres away.
The OVD-Info group, which monitors political arrests, said at least 37 people were arrested at Vnukovo, although their affiliations were not immediately clear.
Vnukovo stopped journalists from entering the terminal last week, saying it was because of fears over Covid-19. The airport also blocked access to the international arrivals area.
Last month, the opposition figure released the recording of a phone call he said he made to a member of a group of officers from the Federal Security Service (FSB), who he claimed poisoned him in August and then tried to cover it up. The FSB dismissed the recording as fake.
The governments of Latvia, Lithuania and Estonia warned Russia to release Mr Navalny or face the prospect of new EU sanctions.