Five staff members at Minnesota's maximum security prison were injured in an apparent fight on Friday night.
The Minnesota Department of Corrections confirmed to BMTN that five staff members at MCF–Oak Park Heights, near Stillwater, were taken to hospital and subsequently released.
"It's actively under investigation so I can't release any other details at this time," the DOC added, though the Pioneer Press reports they were involved in a "melee" with an unknown number of inmates.
MCF-Oak Park Heights opened in 1982, and according to the DOC website it has a capacity of up to 473 inmates.
It's the state's only maximum-security prison, holding the highest custody level in the DOC system.
The majority of those held there are classified as maximum custody or "extreme risks to the public."
It also has a medical infirmary that handles health care needs for offenders transitioning from other facilities, and a mental health unit for offenders with severe mental health needs.