Updated

At least 12 prison guards are being held hostage amid a prisoner uprising in southern Brazil.

The uprising at the Guarapuava prison housing nearly 250 inmates began Monday when inmates on a work detail over-powered guards. There was no word yet on injuries.

Live television images showed hooded prisoners armed with knives and clubs on the roof of a prison building, making threatening gestures toward disrobed guards, whose hands were tied behind their backs.

The Parana state justice secretariat, in charge of prisons, says its director is negotiating directly with the inmates holding the guards captive. An official with the secretariat said inmates are asking for better conditions, but didn't know specifically what they demanded.

Brazilian prisons are severely overcrowded and uprisings, often bloody, are frequent.