Russian opposition leader Alexei Navalny was being held in a Moscow police cell on Monday after his dramatic airport arrest, as calls grew in the West for his immediate release.
President Vladimir Putin's most vocal critic was still waiting to see his lawyer hours after being taken away at border control following a flight from Germany where he was recovering after a near-deadly poisoning attack.
He was picked up by police on arrival, prompting a wave of Western condemnation, with foreign governments and activists urging the Kremlin to release Navalny.
German Foreign Minister Heiko Maas said Monday it was "totally incomprehensible" that the Russian authorities arrested Navalny and called on Russia to "immediately" release him.
Navalny "took the conscious decision to return to Russia because he sees it as his personal and political home", Maas said.
A close Navalny ally said early Monday that the opposition politician was being held in the town of Khimki just outside Moscow and that a member of his defence team could see Navalny during the morning.
"They are now allowing a lawyer in," Leonid Volkov wrote on Twitter.
Navalny was detained at Moscow's Sheremetyevo airport less on arrival from Germany where he had been recovering from a nerve agent attack he says was carried out by the FSB domestic intelligence on Putin's orders.
The United States, the European Union, several EU governments, Canada and a senior aide to US President-elect Joe Biden immediately called for his release, with some in the EU urging new sanctions against Moscow.
Rights groups joined the calls, with Amnesty International saying Navalny had become a prisoner of conscience.
European Council president Charles Michel said Navalny's detention was "unacceptable", while the French foreign ministry said the arrest caused "very strong concern".
Russian foreign ministry spokeswoman Maria Zakharova hit back telling foreign leaders to "respect international law" and "deal with the problems in your own country".
Navalny, 44, was met by uniformed police at passport control after his Berlin flight touched down in Moscow.
He embraced his wife Yulia who was travelling with him and was led away.
Russia's FSIN prison service said on Sunday it had detained Navalny for "multiple violations" of a 2014 suspended sentence for fraud, adding that "he will be held in custody" until a court ruling.
Speaking to journalists at Sheremetyevo before his detention, Navalny said he did not fear being arrested.
"I know that the criminal cases against me are fabricated," Navalny said, standing in the terminal in front of a picture of the Kremlin.
His plane landed at Sheremetyevo after a last-minute diversion from another Moscow airport, Vnukovo, where hundreds of supporters and media were waiting.
Several of his associates were taken into custody at the airport while the plane was in the air, including prominent Moscow activist Lyubov Sobol and other top aides.
OVD Info, which monitors detentions at political protests in Russia, said that around 70 people had been detained.
Sobol and others later said they were released and were facing administrative charges.
Navalny fell violently ill on a flight over Siberia in August and was flown to Berlin in an induced coma. Western experts concluded he was poisoned with Soviet-designed nerve toxin Novichok.
The Kremlin denies any involvement and Russian investigators say there are no grounds to launch a probe.
Navalny has been the symbol of Russia's protest movement for a decade after rising to prominence as an anti-corruption blogger and leading anti-government street rallies.