Two prison officers in Mountjoy jail in Dublin have been injured after being attacked by a prisoner on Thursday.
It is understood the prisoner used a shiv, or homemade knife, to assault the officers when they came to open his cell shortly after 8.30am.
One of the officers received a stab wound to the head while the second sustained wounds on his back and chest.
The Irish Prison Service said the officers had been taken to hospital with "slash wounds, which while serious, are not thought to be life threatening".
The attack took place in the Challenging Behaviour Unit in the basement of Mountjoy. It is understood the inmate who carried out the attack was being held there for spitting at a nurse.
This inmate is serving a four-year term for aggravated burglary and started their sentence in September 2014.
The Irish Prison Service has started an investigation and gardaí have been notified.
The director general of the Irish Prison Service has said his thoughts are with the injured staff and their families.
Prison officers in Irish jails do not currently wear stab vests while at work although is due to change shortly.
