Russian opposition leader and a critic of President Putin Alexei Navalny was on Sunday detained after he flew back to Moscow from Germany, five months after he was nearly killed by a nerve agent attack.
The activist, 44, was led away by police at passport control at Sheremetyevo airport a soon as his plane landed, BBC reports.
Thousands of his supporters had gathered at the Moscow airport to greet him on his return from Berlin, but anticipating trouble the authorities diverted his plane.
Mr Navalny has blamed Russian authorities for trying to kill him by administering him poison, a blame the Kremlin has denied consistently.
But Mr Navalny's allegations have been backed up by reports from investigative journalists and by his medical reports.
As news of Mr Navalny's detention spread it led to condemnation from the European Union, France and Italy, and they all called for his immediate release.
The same calls were echoed by the incoming Biden administration in the US.