In the footage, which prosecutors say appears to have occurred at Detention Center-4 in Kemerovo in 2017, guards are seen lining up and beating detainees after they are led out of a cell that is being searched.
The gulagu.net human rights portal originally published the video after it said it was sent via a video-sharing hotline on December 28.
The group alleges beatings, humiliation, and other physical abuse in addition to overcrowding at the facility.
The Kemerovo Prosecutor-General’s Office announced its investigation on January 3.
Interfax reported that an internal investigation had already been conducted and “persons involved in this incident were brought to strict disciplinary accountability.” It did not specify what disciplinary measures had been taken but said “instructions have been issued to prevent similar events from happening in the future.”
There have been mounting cases of video unearthed by lawyers or rights groups demonstrating violent prisoner abuse in Russia’s harsh penal system.
The head of a prison in the northwestern region of Karelia was suspended in October after 5-year-old video emerged that contradicted his denials of prisoner mistreatment there.