Activists stood in protest during the opening remarks of the Russian representative at the annual meeting of the Organization for Security and Cooperation in Europe in Warsaw on Monday.
The two-week meeting, focused on human rights, is a rare forum where civil society and governments participate equally.
Many participants from civil society wore T-shirts or had big stickers on their backs saying #SaveOlegSentsov.
Sentsov, a Ukraine native of the Russia-annexed Crimea Peninsula, was sentenced to 20 years in prison in 2015 for conspiracy to commit terrorism. His supporters call the prosecution of Sentsov, who staunchly opposed the annexation, politically motivated.
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