The Council of Europe's Committee for the Prevention of Torture has criticised the detention in prison of psychiatric patients and immigrants refused the right to remain in Ireland.
The Committee published its latest report on Ireland following a visit to a number of prisons and garda stations in September of last year.
It also said it received a number of allegations of ill-treatment by prison officers and gardaí, the majority against gardaí at the time of or shortly after arrest.
The Committee also criticised the prison service for gang violence in the prisons and said some inmates were being detained in conditions akin to solitary confinement.
The Committee found that immigrant detainees at Cloverhill Prison were held with remand and convicted prisoners and, in some cases, subjected to bullying.
It reiterated that prison was not a suitable place for someone neither suspected nor convicted of a crime, and specifically criticised the detention of the mentally ill in prison.
The Committee also found that while the majority of detained persons it interviewed said they were treated correctly by prison officers and gardaí, some alleged they had been physically mistreated and verbally abused.
The Prison Service was also criticised for the level of prisoner violence due to gangs and drug use and for the sanction of "loss of all privileges" which was compared to solitary confinement.
The Government pointed out that many inmates were on restrictive regimes for their own safety and that the numbers on them had since been reduced.
The Government said it expected to have a dedicated immigrant detention facility at Dublin Airport next year and new mental health facilities by 2018.
It said that it was "disappointed" and that gardaí and prison staff were well aware of their obligations.
