The man suspected of revealing classified US government documents to the WikiLeaks website is being held in solitary confinement while awaiting trial.
Bradley Manning has been kept alone in his cell in a Virginia jail for 23 hours a day, under constant surveillance, for seven months.
The Pentagon denies he is being mistreated, sying that he receives visitors, can make phone calls, and routinely meets with doctors.
But the UN says the use of solitary confinement for prolonged periods can be a form of torture that should be used sparingly.
Al Jazeera's Kristen Saloomey reports from the Quantico military base.