In a statement on Thursday, the Arizona Department of Corrections, Rehabilitation and Reentry said the riot began after several hundred inmates grouped together around staff and refused to disperse since Wednesday, Xinhua news agency.

The prison was still on lockdown as of Thursday afternoon.

Local KJZZ radio station said families of the inmates reported pepper balls and rubber bullets were fired at the prisoners, the rioters were zip-tied and held on a yard, while officials searched their living areas.

According to KJZZ, emails from inmates living at the unit said windows had been broken on the property and one inmate wrote that the unit looked like it had "exploded".

"They came in with tear gas, flash bangs, pepper spray, and started shooting at everyone," the inmate wrote.

"It was basically a war zone."

The Department did not reveal the cause of the riot.

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