The head of an Oklahoma prison workers group says the stabbing deaths of four white inmates at a private prison in Cushing were the result of violence between two white prison gangs that also spilled over into other state prisons.

Oklahoma Corrections Professionals Director Sean Wallace says Saturday's killings resulted from a feud between the Irish Mob and the Universal Aryan Brotherhood. Wallace says on the same day the deadly stabbings took place at the Cimarron Correctional Facility, there were large fights at two other state prisons and a stabbing at the Oklahoma State Reformatory in Granite.

Neither the Department of Corrections nor the company that runs the Cushing prison — Tennessee-based Corrections Corporation of America — would confirm a motive for the stabbings, which are under investigation.