A 34-year-old man is in a critical condition in hospital in Dublin after he was attacked and severely beaten by a group of other prisoners in Mountjoy Prison.

The inmate was attacked in his cell at around 6pm yesterday evening and sustained serious head injuries.

He was taken to the Mater Hospital, where he is in intensive care.

Gardaí suspect the attack was ordered by a criminal outside the prison.

The cell and landing area in Mountjoy where the inmate was attacked remains sealed off today for a forensic examination.

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The man had been sentenced to six-and-a-half years in prison just two days before the attack.

He pleaded guilty after he was caught with a loaded semi-automatic pistol and a magazine with three more rounds in Dublin last year.

He was already in prison for a different crime in Mountjoy since February.

A threat assessment was carried out in Mountjoy and he was initially moved from one part of the prison to another after an issue arose.

However, prison sources said the man expressed no fears for his safety and was not put in protective custody.

Gardaí at Mountjoy are carrying out a criminal investigation and will seek to interview prison staff and inmates.

The prison has CCTV and detectives believe they may be able to secure footage of the men suspected of carrying out the attack on the prison landings and entering the man's cell.

They also believe the attack was ordered from outside the prison either because of the inmate’s drug debt or because of the foiled gun attack for which he was jailed.

The prison service said in a statement that it could "confirm that a prisoner was seriously injured during an incident in Mountjoy Prison yesterday. The matter is subject to a garda investigation".