CUSHING, Okla. » Three inmates are dead and five injured after a disturbance at an Oklahoma prison, a spokesman for a company that owns and operates the facility said Saturday.

Staff at Cimarron Correctional Facility in Cushing quelled an inmate disturbance around 4:40 p.m. Saturday, said Steve Owen of Nashville, Tennessee-based Corrections Corporation of America. He said in a release that the incident lasted about 40 minutes and was contained to one housing pod.

No staff members were injured. The inmates who were hurt were taken to hospitals. It’s not clear what caused their injuries.

The names of those killed and injured were not immediately released.

Owen said the prison was placed on lockdown and inmates confined to their housing areas. The facility about 50 miles southwest of Tulsa in northeast Oklahoma houses medium- and maximum-security male inmates for the Oklahoma Department of Corrections.

The incident occurred in a medium-security portion of the prison, Department of Corrections spokeswoman Terri Watkins told The Associated Press. The prison houses about 1,600 inmates, she said.

Owen said the incident remains under investigation.

Corrections Corporation of America, one of nation’s largest private prison companies, contracts with various states and other entities to house inmates.