The International Committee of the Red Cross (ICRC) has confirmed that it has for the first time visited terrorism suspects recently transferred to Guantanamo.
The Swiss-run humanitarian body said that it had seen 454 prisoners from some 40 countries during its latest three-week visit to the United States' detention facility in Cuba.
This number included 14 men previously held by the CIA and recently transferred, according to ICRC spokesman Vincent Lusser.
Among the 14 detainees are the suspected mastermind of the September 11, 2001 suicide plane attacks - Khalid Sheikh Mohammed - and two other al Qaeda leaders, Ramzi Binalshibh and Abu Zubaydah.
The encounters apparently mark the first time the 14 have met anyone other than their captors since they were arrested and held in custody at secret locations.
The Pentagon, which said on Thursday that the ICRC had been granted access to the men for the first time, has described them as "some of the world's most dangerous and vicious individuals".
"The key thing is we were able to register them, which means that once they are in our system we are going to follow up on them all the time of their detention," Lusser said.
All the detainees had had the opportunity to send Red Cross messages to their families, he added.
In exchange for access to detainees worldwide, the ICRC keeps its findings confidential, sharing them only with detaining authorities.
The organisation welcomed the access it was given to the 14 newest prisoners at Guantanamo. It has been trying to obtain access to US detainees in undisclosed locations for a long time.
Under the Geneva Conventions on the conduct of war, ICRC delegates are supposed to have access to all prisoners of war. Officials had been aware of the arrests of some detainees months or years ago, but never came across them in the US prisons it visits despite repeated requests to see them all.
United Nations human rights bodies have called for the closure of Guantanamo - where detainees have been held indefinitely without charge - as well as of secret prisons where they say inmates are vulnerable to mistreatment.
US officials said last month the CIA had held fewer than 100 suspects in secret detention centres and that after the transfer of the 14, it held none.
Asked if the ICRC was convinced there were no more suspects being held secretly, Lusser said: "We are reassessing the situation following the recent US declaration. We would be concerned if the programme were to be maintained or resumed."
swissinfo with agencies
The ICRC has been visiting people detained in connection with armed conflicts since 1915 when its delegates first negotiated access to tens of thousands of prisoners of war held during World War One.
The organisation has been conducting regular visits to Guantanamo since 2002, usually 12 times per year.
The ICRC regularly discusses its findings concerning US detention facilities with the military authorities in the camps as well as with the appropriate US government officials in Kabul and Washington.
Despite occasionally going public with its concerns, such as the legal status of detainees, the ICRC continues to maintain a direct and confidential dialogue with the US authorities.