A prison officer has been slashed across the buttock with a makeshift knife at Midlands Prison.
Two of his colleagues were hospitalised after a separate attack in the prison this morning.
The incidents, which were separate but related, occurred on the sex offenders' E landing of the prison in Portlaoise, Co Laois.
The attacks come just weeks after two officers were stabbed by bank robber Derek Brockwell (53) as he escaped while under escort from Portlaoise Prison to Tallaght Hospital, Dublin, where his diabetes was being assessed.
The latest violence has also occurred during an industrial dispute between the Irish Prison Service and the Prison Officers’ Association.
The association is to ballot its members on industrial action in a row of staffing levels in prisons.
The officer slashed across the buttocks at the Midlands Prison this morning was injured when he and two colleagues moved in to prevent two prisoners attacking another inmate on a stairwell at around 11am.
One of the prisoners stabbed the officer with a makeshift knife, known as a shiv in the prison setting, before the aggressors were overpowered by staff and the weapon seized.
And when that flashpoint was contained and senior staff were interviewing prisoners to establish how the earlier incident had occurred, one of the prisoners being questioned lashed out at three other officers.
“He had to be subdued and two of the officers involved in overpowering him were injured,” said one prison source.
They were taken to nearby Portlaoise Hospital when one was treated for a suspected broken ankle and the other for twisted knee. Their colleague who had been slashed across the buttock had already been taken to the hospital for treatment and required about 15 stitches.
The outbreak of violence in a section of a prison that only houses sex offenders is unusual. Such prisoners are regarded as the most compliant of any offender group.
Prisons or sections of jails housing them generally have the lowest level of violence or contraband, such as weapons, drugs and mobile phones, in circulation.
Prison sources said the identity of the two prisoners who were about to attack the third inmate on the stairwell when staff intervened has been established and they have been isolated.
One is related to a much younger man jailed in another prison for a high profile killing in recent years.
The man who later lashed out at senior prison staff conducting prisoner interviews about the first attack, has also been placed into isolation. He had been involved in a number of disciplinary incidents recently in the Midlands Prison and had just been informed he was being transferred off the E landing.
The Irish Prison Service believes his dissatisfaction at being transferred was the motivation for his actions today. A spokesman for the service said it was aware of both incidents at the jail. He confirmed three officers had been hospitalised.
He added they had been discharged and that investigations into what had occurred were ongoing.