Some inmates were spending 23 hours a day in their cells
Inmates at Hydebank prison in south Belfast have had to endure "appalling conditions", a report has found.
The Independent Monitoring Board found inmates were "helpless pawns" in the poor working relationship between the Prison Service and its staff.
It criticised the number of occasions prisoners were confined to their cells, disputing the prison authority's defence staff shortages were to blame.
Some were spending 23 hours a day in their cells four or five days in a row.
This happened during a four-month industrial dispute in 2007.
Hydebank Wood Young Offenders Centre in south Belfast, accommodates male prisoners aged from 16 to 21. It shares a site with Northern Ireland's women's prison.
"The women and young men had to endure appalling living conditions," the report found.
"In several cases, on account of enforced cell-sharing, two young men confined to a small cell designed for one, for many consecutive days and had to consume all their meals in a very restricted space that contained a lavatory bowl.
"The IMB considers that the duration and frequency of use of cellular confinement and loss of association were excessive and were indicative of a punitive regime."
It added: "Many of those locked away from their peers in solitary confinement appeared to be mentally ill or personality disordered."
The report claimed there was too much emphasis on security and control at the prison and identified a need to focus "much more on the rehabilitation and resettlement of prisoners".
It blamed a new shift pattern and an investigation into alleged overtime fraud as the main factors in lowering staff morale.
'Cultural awareness training'
The IMB recommends that due to "the marked over-representation of Protestants in the Hydebank workforce and the majority of the prisoner population being Catholic, it would be beneficial for staff to receive cultural awareness training in respect of the Catholic community in Northern Ireland and how it differs from the Protestant culture".
It concluded that it was disappointed that number of "constructive recommendations" in last year's report were not implemented.
Reacting to the report, the Prison Service said it would publish its full response shortly.
However, it claimed the report was "dated and refers in particular to a time in the summer of 2007 when there were higher levels of staff sickness at Hydebank Wood which resulted in some restrictions to the normal regime".