The US airbase at Bagram in Afghanistan contains a facility for detainees that is distinct from its main prison, the Red Cross has confirmed to the BBC.
Nine former prisoners have told the BBC that they were held in a separate building, and subjected to abuse.
The spokesman was responding to a question from the BBC about the existence of the facility, referred to by many former prisoners as the Tor Jail, which translates as "black jail".
In recent weeks the BBC has logged the testimonies of nine prisoners who say they had been held in the so-called "Tor Jail".
They told consistent stories of being held in isolation in cold cells where a light is on all day and night.
The men said they had been deprived of sleep by US military personnel there.