Two separate investigations into a protest at Cloverhill Prison in West Dublin earlier will be carried out by gardaí and the Irish Prison Service.
One prisoner was seriously injured during the incident, which began this morning when a group of inmates refused to return to their cells after exercising.
Two prisoners climbed onto the roof and refused to get down.
Despite efforts by prison officers to resolve the situation, one prisoner assaulted and seriously injured another inmate.
Members of the control and restraint teams went into the yard to remove the remaining 15 prisoners, some of whom were injured.
Five ambulances were seen leaving Cloverhill after the incident.