Putin critic Alexei Navalny has been detained after flying 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.
Thousands had gathered at a different Moscow airport to greet his flight from Berlin, but the plane was diverted.
Mr Navalny blames Russian authorities for the attempt on his life last year. The Kremlin denies any role.
The opposition politician’s allegations have however been backed up by reports from investigative journalists.
“I know that I’m right. I fear nothing,” Mr Navalny told supporters and the media upon landing, just minutes before he was detained. “Have you been waiting for me long?” he asked border guards.