Convicted killer Freddie Thompson has brought a High Court challenge over what he claims is the "extremely oppressive" and "severe" regime he is being subjected to at Portlaoise Prison.
Thompson (39), from Dublin's south inner city, is serving a life sentence handed down last year after his conviction at the Special Criminal Court for the murder of David Douglas in 2016.
He also claims his treatment in prison stems from the authorities' belief he was involved in a feud with fellow prisoner Brian Rattigan.
In a sworn statement, Thompson, who was not in court, said he was "informally told" he had been moved to his current location because of a perceived feud with Rattigan.
He said that after he was sentenced he "agreed to meet with Rattigan" in a meeting he said was "facilitated by the prison authorities".
"I sat down and talked with Mr Rattigan, who I have only ever met once in person on one previous occasion," he said.
"I say that we spoke at length about how the media had fuelled the idea of a raging feud between us.
"I say that we both agreed that there would be no animosity between us into the future," said Thompson, adding he also met with Rattigan on a second occasion.
"Contrary to what is alleged by the prison, I am not involved in a feud with Mr Rattigan and any attempt by the prison authorities to use this as an excuse to justify the current conditions of my detention is not correct.
"The prison authorities are acutely aware of the meetings between us and they are aware that there is no feud ongoing between us," he said, adding that it "may suit the prison's agenda" to claim there is a feud so that they can "keep me in conditions that violate my rights".
Thompson has been serving his sentence in Wing A4 of Portlaoise Prison, which is known as the punishment block, since March 2018.
He claims that, in breach of his human rights, he is only allowed contact with two other prisoners and spends most of his time effectively on "lock-up" in his cell.
He also claims he is being denied regular exercise, fresh air and appropriate education, which also amounts to a breach of his rights and of prison rules.
He claims he was placed on rule 62 of the prison's rules, which allows for the removal of prisoners from structured activities, without reasons other than to ensure good order and security in the prison.
However, he claims he was taken off rule 62 some months ago but there has been no improvement to his conditions or his regime.
He claims that, prior to his move to Portlaoise Prison, he had always been housed within the general prison population.
He also claims he is being treated differently to other prisoners serving life sentences.
At yesterday's sitting of the High Court, lawyers for Thompson started judicial review proceedings against the governor of Portlaoise Prison, the Irish Prison Service and the Justice Minister, aimed at ending his detention away from the mainstream prison population.
His counsel, Padraig Dwyer SC, appearing with Keith Spencer BL, told the court his client's situation "is unbearable" and his mental health has been affected, and that his client is suffering from depression.
In correspondence to Thompson's solicitors, the governor and Irish Prison Service denied Thompson's prison regime is oppressive, and said the regime meets all the statutory requirements.
They say Thompson has been provided with access to facilities including the school, gym, recreation, open-air exercise and other services.
They also say Thompson requested relocation to his current location and that he cannot mix with certain other prisoners due to security issues.
These issues can restrict access to various services within the prison at times, the defendants stated in written replies to Mr Thompson's solicitors, Niall O'Connor & Co.
In his judicial review proceedings, Thompson seeks various orders and declarations including an order quashing his ongoing detention in A Block in Portlaoise Prison, away from the mainstream prison population.
He also seeks declarations that the decision to hold him in A Block amounts to a breach of his constitutional rights and is in breach of various prison rules.
Permission to bring the challenge was granted, on an ex-parte basis, by Ms Justice Teresa Pilkington. The judge made the matter returnable to a date in September.