Independent prison monitors have uncovered widespread abuse at several prisons and detention centers in St. Petersburg that they say are part of a broader pattern of ill-treatment.

Allegations of torture in correctional facilities across Russia have gained national attention after a leaked video showed the violent beating of an inmate at a prison in Yaroslavl. A number of prison guards and wardens have since been detained and some convicted, while the Federal Prison Service vowed to launch a nationwide inspection of correctional facilities.

The St. Petersburg branch of the prison watchdog Public Monitoring Commission (PMC) published excerpts of its field report detailing alleged violence and “inhuman conditions” dating back to 2015. The abuse includes beatings, torture using electric shock and the systematic ignoring of complaints from detainees.

“This is very alarming, since it could mean that the prisoners are intimidated or don’t feel safe to report abuse, and are afraid of being plaintiffs or witnesses,” the group detailed in a report released Monday on the Team 29 legal association’s website.

Its authors say they are convinced the 13 cases documented in the report are “only a small part” of a larger pattern of abuse, with most allegations coming in anonymously.