A man in his 20s is seriously ill in hospital following an incident at Mountjoy Prison in Dublin.
The Irish Prison Service confirmed that a prisoner was involved in an incident with another prisoner yesterday evening. It could not confirm further details of that incident, however.
He was treated by the healthcare staff for superficial injuries, the prison service said in a statement.
At about 10pm he advised staff that he was feeling unwell and he was referred to the nearby Mater hospital "as a precaution".
He was triaged by medical staff.
"At midnight he declined further treatment and asked to be returned to the prison," the statement added.
"At 7.50am this morning the healthcare staff were called to the cell and administered treatment. An ambulance was immediately called and he was taken to the Mater hospital. His condition is described as serious."
The Irish Prison Service and An Garda Siochána are conducting separate investigations into the incident.
It is understood the man sustained what appeared to be a minor wound to the head after a disagreement with the other prisoner. It is also understood he was unconscious when staff at the prison found him this morning and that he has now been transferred to Beaumont Hospital.