The federal prison ombudsman says mentally ill offenders should never be locked up alone for long periods.

Howard Sapers, the correctional investigator, also recommends round-the-clock health-care coverage at medium- and maximum-security prisons.

Sapers has released an extensive report on the Correctional Service's response to deaths in custody.

He has harshly criticized the prison service over the 2007 death of 19-year-old Ashley Smith, who choked herself with a strip of cloth at the Grand Valley prison in Kitchener, Ont.

Last December, Sapers asked the service to clearly spell out what it's doing to help the mentally ill behind bars.

He requested updates on initiatives including treatment plans and the hiring of mental health professionals.

Sapers argues offenders with mental disorders — especially those who might harm or even kill themselves — should not be put in isolation cells.

In March the Correctional Service promised to more closely monitor offenders with mental-health problems placed in segregation.

Ten to 12 per cent of offenders entering the federal prison system have a significant mental problem.