STORMONT ministers have launched a review of how vulnerable prisoners are monitored in prisons following recent suicides and self-harm incidents.
Justice Minister Claire Sugden and Health Minister Michelle O'Neill are jointly undertaking the probe.
Five people have died in custody in the last 12 months - including two in recent weeks.
Life sentence prisoner Barry Cavan from north Belfast and remand prisoner Gerard Mulligan from Lisburn, both took their own lives in the jail.
Prison authorities were also heavily criticised in a report by the Prisoner Ombudsman after inmate Sean Lynch inflicted extreme self-harm on himself in Maghaberry high security jail in June 2014.
Ms Sugden said full investigations of the suicides inside Maghaberry were ongoing and officials were also endeavouring to develop a "community response plan" to prevent further deaths. She said the Prison Service's suicide and self-harm policy was also being re-examined.
The minister outlined to the assembly the extent of mental health issues in prisons.
"On 17 November 2016 the prison population totalled 1,533, of these 417 were recorded as having a mental health illness and a further 740 prisoners recorded as having an addiction," she said.
"The needs of those in prison are complex, and in comparison to wider society, there are disproportionately higher numbers of prisoners who present with mental health problems and personality disorders. In addition, the problems associated with alcohol and substance misuse, mental illness and generally poor coping skills are all higher.
"Research also tells us that people in custody are more likely to have either undiagnosed or unmet health needs. For many their first mental health diagnosis occurs only when they are in custody."
The minister added: "However we portray it, the custody environment is not designed to deal with those experiencing severe chronic mental health issues. Whatever level of training we provide to staff, they remain prison officers.
"The Northern Ireland Prison Service (Nips) cannot meet this challenge alone, we need the ongoing help and support of the Department of Health, other departments, and partners across the justice system, and in the wider community.
Prison officers, she added, played a vital role in assessing and supporting vulnerable offenders during periods of crisis.
"Countless lives have been saved by prison officers who identify prisoners at risk and care for them successfully," she said.
"The management of the Prison Service, governors and their teams work tirelessly to reduce the rate of self-harm and to prevent suicide. Identifying and supporting prisoners with mental health issues remains a high priority for Nips. However, not every episode of self-harm can be prevented and tragically, some suicides will happen despite the best efforts of staff."