Seven republican prisoners at Portlaoise Prison, Co Laois, were hospitalised yesterday after an early morning fight at the prison during which rival dissident republican factions clashed.
A fight between two inmates escalated, resulting in a much bigger group becoming involved in serious clashes for around 30 minutes.
The Irish Prison Service said around 12 to 14 inmates were involved in the incident.
However, other prison sources said there were up to 30 inmates involved and that some had used the legs of tables and chairs as weapons as well as brush handles.
The injured inmates were taken to Portlaoise Hospital at different times during the day
"It took the staff more than 30 minutes to regain control," said one prison source.
"Back-up was needed from other areas of the prison and the whole place was locked down for a number of hours."
The hospitalised prisoners all sustained head injuries, mainly heavy bruising and cuts to the face.
No staff were injured, according to a spokesman for the Irish Prison Service.
The inmates involved will each be called before the governor, Mr T. J. Walsh, to account for their role in the incident. They face the loss of privileges and remission.
The outbreak of violence at the jail comes at a time when tension between rival republican dissident factions remains high. Those involved in the ongoing dispute have divided into two camps.
One faction is loosely based around "Real" IRA leading figure Liam Campbell while the other prisoners have allied themselves to Michael McKevitt, another leading member of the same organisation. Neither McKevitt nor Campbell were involved in yesterday's fight.
Tension has mounted in the prison in recent times as one side has accused the other of being more interested in engaging in criminal activity rather than continuing to pursue their republican goals once released from prison.
In an effort to calm the situation, Campbell was transferred from the E2 landing to the E3 landing last year.
Yesterday's trouble began when cells were unlocked on the landings at 8.45 a.m.
There was a verbal exchange between two of the 40 republican inmates on the landings and the two men quickly became involved in a physical fight. Others then joined in as the incident rapidly escalated.
After the fight was brought under control, the two inmates who had sustained the worst injuries were taken to hospital immediately. All prisoners were then locked in their cells until early afternoon and restricted visiting arrangements were put in place.
Ambulances called to the prison at different times during the morning to bring the other five injured men to hospital.
The prison service said it did not want all of the injured prisoners at the hospital at the same time for fear they would become involved in a further confrontation. All seven prisoners were returned to the jail after undergoing treatment.
Mr Eugene Dennehy, deputy general secretary of the Prison Officers' Association, said a meeting was being sought with prison authorities.
McKevitt (54), Beech Park, Blackrock, Co Louth, was jailed for 20 years in August 2003 for directing the activities of a terrorist organisation and for membership of an illegal organisation.
Campbell (41), Upper Faughart, Dundalk, Co Louth, was sentenced to eight years imprisonment last May for membership of the "Real" IRA on dates in 2000 and 2001.
