Police detained Kremlin critic Alexei Navalny on Sunday when he flew back to Russia months after barely surviving a poisoning attack. The arrest has prompted a wave of Western condemnation.
Navalny was detained at Moscow's Sheremetyevo airport less than an hour after he flew in from Germany, where he had been recovering from the poisoning which he claims was ordered by Russian President Vladimir Putin.
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 and accusing the Russian authorities of waging "a relentless campaign" to silence him.
French foreign ministry 'concerned'
European Council president Charles Michel wrote on Twitter that Navalny's detention was "unacceptable", while the French foreign ministry said the arrest caused "very strong concern".
"Mr Navalny should be immediately released, and the perpetrators of the outrageous attack on his life must be held accountable," Joe Biden's national security advisor Jake Sullivan tweeted.
France condemns Navalny poisoning as Kremlin denies involvement
US Secretary of State Mike Pompeo added that America "strongly condemns" the arrest, noting with "grave concern" that Navalny's detention was the latest attempt to silence voices critical of Russia's government.
Russia warns the world to back off
Russian foreign ministry spokeswoman Maria Zakharova hit back in a Facebook post, telling foreign leaders to "respect international law" and "deal with the problems in your own country".
Navalny 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, with aides later saying he was being held at police station near the airport.
"Alexei was detained without the reason being explained," Navalny's lawyer Olga Mikhailova said at the airport, adding that she had been refused the right to accompany him.
"Everything that is happening now is against the law."