Three inmates are dead and five are injured, following a disturbance at a correctional facility Oklahoma on Saturday. 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 40-minute disturbance at Cimarron Correctional Facility was 'quelled' by staff around 4.40pm local time (11:40 BST). Facility staff members were hurt, according to Steve Owen of Nashville, Tennessee-based Corrections Corporation of America.

The injured inmates were taken to hospital for treatment. The cause of their injuries remain unclear. The names of the dead and hurt inmates have not been released, but the families of those killed have been contacted.

The disturbance occurred in one housing pod, and the prison was placed on lockdown, leaving inmates confined to their housing areas on Saturday. Owen said that law enforcement and prison management are investigating the incident.

Around 180 prisoners are considered "maximum security" prisoners at the Cimarron facility, meaning that they are an escape risk or convicted of a particularly heinous crime, or both. Whether the brawl occurred in a maximum security housing pod is still not known.

Corporation-run prison

Cimarron Correctional is a 1,720-bed facility and houses medium- and maximum-security inmates for the state corrections system, Owen said. It is run by the private company Corrections Corporations of America (CCA).

CCA operates four correctional facilities in Oklahoma. It manages prisons and other facilities in 20 states, and calls itself "the nation's fifth largest corrections system".

Between 200-300 inmates were involved in a brawl in June at the same prison when fighting broke out among inmates in three separate housing units. Eleven prisoners were taken to hospital after the fight, although no correctional workers were injured, the Associated Press reported.

US prison conditions

Gang activity in US prisons poses a major security problem, as many prisoners belong to rival gangs, such as Bloods, Crips and MS-13, in which members gain status and respect for injuring and killing other inmates or correctional officers, according to website Inquisitr. Because of this, weapons are sometimes smuggled into prison facilities from the outside.

While correctional officers are trained in riot situations, many prisons operate with a very high prisoner-to-guard ratio, leaving guards vulnerable to attack and in a difficult situation when fights break out. Inmates are usually placed on lockdown when a disturbance may be on the horizon, before riots or injuries occur. Prisons are obliged to protect their inmates, but can be difficult to maintain when thousands of violent offenders are housed in close quarters.

In 2009 California was found guilty by US federal court for failing to provide even "the minimal civilized measure of life's necessities". In the words of the court, the state's prisons were "bursting at the seams," with conditions so dire that "a California inmate was dying needlessly every six or seven days".

US inmate Hugo Pinell, the last member of the "San Quentin Six", was killed in a jail yard riot by another inmate at maximum security California State Prison-Sacramento.