The hearing was to consider a motion by the federal prison authority to replace a controversial 2014 suspended sentence handed to Alexei Navalny with a jail term.
Allies of Navalny called on his supporters to gather outside the court on Tuesday morning, Radio Free Europe/Radio Liberty said.
This footage was recorded by the filmmaker Danila Gulin and shows him and other detainees in the back of a police vehicle, and being processed at a building. He told Storyful had not been released by 3:30 pm local time. Credit: Danila Gulin via Storyful