"Yesterday he was placed in the special unit of the Butyrskaya prison, also known as Detention Facility No. 2. He is still there," the source said.
Ukrainian filmmaker Oleh Sentsov, who had been convicted of terrorism, was transferred to Moscow's Detention Facility No. 2, also known as the Butyrskaya prison.
Sentsov, a Crimean native who opposed Russia's 2014 takeover of the Ukrainian peninsula, is serving a 20-year prison term after being convicted of terrorism in a trial that he, human rights groups, and Western governments contend was politically motivated.