Gardaí are investigating the circumstances surrounding the death of a 35-year-old inmate in Portlaoise Prison.
The man, who was a member of the Continuity IRA, was found in a wardrobe in his cell just after 10.30am this morning.
He was serving five years for possession of firearms and was due out in 2008. He was found dead by another prisoner.
The body was found in a metal wardrobe in his single cell, which is in the E4 Wing of the prison, which houses dissident republicans.
His cell had been unlocked by officers this morning and he appeared to be still asleep. But subversive inmates at Portlaoise have a certain freedom of movement and control of their own affairs so the man would not have been ordered out of bed.
Gardaí have sealed off the landing and forensic teams are carrying out an investigation at the scene.
The man was arrested at a Continuity IRA camp where firearms, ammunition, balaclavas and a makeshift firing range were found.
The Prison Service has said the Governor will carry out an inquiry into the circumstances of the man's death.