A federal investigation into a Virginia jail where several inmates have died says the jail failed to provide adequate medical treatment and mental health care.

The report released Wednesday said inmates with serious mental illness are kept in cells for the "vast majority" of each day.

Investigators said conditions at the Hampton Roads Regional Jail in Portsmouth violate the U.S. Constitution and Americans with Disabilities Act.

The Department of Justice and the U.S. Attorney's Office for the Eastern District of Virginia conducted the probe. They threatened a lawsuit if the jail doesn't work with authorities to improve conditions.

David A. Hackworth, the jail's superintendent, said it wouldn't be appropriate to comment because he just received the report. But he said the staff strives to provide the best service to inmates.