A report giving details of atrocious conditions in which prisoners are held in Eritrea has been published by the Oslo Centre for Peace and Human Rights.
It alleges that between 10,000 and 30,000 people are held as political prisoners in a country of about five million.
Groups including Amnesty International and Human Rights Watch have described the absolute control exercised by a narrow group around President Isaias Afworki.
But this new report provides chilling details of their means of control, the BBC reports.
Some prisoners are held in shipping containers, others in dungeons deep underground. Torture is routine, with victims hung from their wrists and feet from trees in the sun or the rain.