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 US military says the main prison, now called the Detention Facility in Parwan, is the only detention facility on the base.
However, it has said it will look into the abuse allegations made to the BBC.
The International Committee of the Red Cross (ICRC) said that since August 2009 US authorities have been notifying it of names of detained people in a separate structure at Bagram.
"The ICRC is being notified by the US authorities of detained people within 14 days of their arrest," a Red Cross spokesman said.
"This has been routine practice since August 2009 and is a development welcomed by the ICRC."
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".
"We are being notified about persons at the Bagram Theatre Internment Facility [now Detention Facility in Parwan] since Feb 2008," the ICRC spokesman added.
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.
In response to these allegations, Vice Adm Robert Harward, in charge of US detentions in Afghanistan, denied the existence of such a facility or abuses.
He told the BBC that the Parwan Detention Facility was the only US detention centre in the country.