The Catholic Church in Papua New Guinea says sleep deprivation could be a form of torture being used on asylum seekers detained in Port Moresby's Bomana prison.
Eighteen asylum seekers remain in Bomana where they were locked up in August after seven years on Manus Island.
About 30 have been released, having agreed to return to the countries they fled.
The church's Giorgio Licini told Ben Robinson Drawbridge those set free have spoken of sleepless nights during their internment.
Bomana Correctional Facility, Papua New Guinea Photo: RNZ / Johnny Blades
