Gardaí have arrested a man in connection with the death of another man in Cloverhill Prison yesterday.
Emergency services were called to the scene at around midnight following an incident between two inmates.
The man, who is in his 50s, was arrested at Cloverhill Prison on suspicion of murder.
He is being questioned at Clondalkin Garda Station under Section 4 of the Criminal Justice Act 1984.
It follows the death of a man in his late 30s at the prison in the early hours of yesterday morning, while a second man received minor injuries.
The Irish Prison Service has launched and investigation, and has stressed that all practicable measures are taken by prison management and staff to ensure the safety of those in custody.
However, the IPS did acknowledge that no prison system can be completely free of violence and inter prisoner assaults do occur.
A post-mortem was completed on the man's body yesterday by State Pathologist Doctor Margaret Bolster.
The results will not be released for operational reasons.