Four inmates have died of injuries sustained during a disturbance at an Oklahoma prison, and investigators are trying to determine what provoked the violence, officials said.

The fight at the Cimarron Correctional Facility in Cushing, Oklahoma, began Saturday afternoon and lasted for approximately two minutes, according to a statement from Corrections Corporation of America.

Steve Owen, a spokesman for a private company that owns and operates the facility, said Saturday's disturbance lasted about 40 minutes and was limited to one housing pod.

Three inmates were declared dead on Saturday and the fourth died overnight at a hospital.

Terri Watkins, a spokeswoman for the state Department of Corrections, said Sunday that preliminary reports showed the first three men were fatally stabbed. But Watkins said she didn't know the nature of the injuries to any of the other inmates.

"The entire stabbing incident happened over a couple of minutes," she said, adding that prisoners were all locked in their cells during the violence.

No prison staff were injured or involved in the attack, Watkins said. None of the prisoners' names were released because their families had to be notified first, she added.

Hundreds of inmates were involved in fights and riots at the same facility in June, injuring around a dozen.

According to figures from the Bureau of Justice Statistics, Oklahoma has the highest rate of prison homicides in the nation, with state inmates killed at a rate more than three times the national average.