Alexey Navalny Arrested upon Arrival in Moscow, His Supporters Detained in Airport

Police detained top Kremlin critic Alexey Navalny on Sunday when he flew back to Russia months after barely surviving a poisoning attack, prompting a new 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 with a nerve agent he says was ordered by President Vladimir Putin.

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 Russian authorities of waging "a relentless campaign" to silence him.

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," Biden's national security advisor Jake Sullivan tweeted.

Russian foreign ministry spokeswoman Maria Zakharova hit back in a post on her Facebook page, telling foreign leaders to "respect international law" and "deal with the problems in your own country". 

Navalny, 44, was met by uniformed police wearing black surgical-style masks at passport control after his flight from Berlin touched down in Moscow, according to AFP journalists at the scene.

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.

"Alexey was detained...