High-security prisons across California have tightly restricted movement, calls and visits while officials probe a surge in violence this year.

The day before state authorities announced plans to restrict inmate movement and revoke visits and other privileges, three inmates were killed in attacks at three different prisons.

The California State Prison, Sacramento is among facilities that are being placed on modified movement after a surge in violence, correctional officers said.

Los Angeles County and other state prisons are upgrading their security after a recent surge in violence against staff and inmates. The California Department of Corrections and Rehabilitation (CDCR) announced that it’s placing Level IV high-security sections within its facilities on a modified program,