The head of the International Committee of the Red Cross has criticised the US for refusing to let it visit secret detainees held in the "war on terror".
Reports have alleged the US is running secret jails abroad
Jakob Kellenberger said their names should not be concealed "no matter how legitimate the grounds for detention".
The US has been accused of operating secret prisons and transporting some detainees to states which use torture.
Washington responded to the Red Cross by saying it was not obliged to allow access to all of its detainees.
"There is a certain subcategory of individuals who have forfeited their protections under the Geneva Conventions and there is not an obligation to allow access to those individuals," said state department spokesman Sean McCormack.
The US has admitted to some use of third countries but says prisoners are never transferred for the purpose of torture.
Both the United States and a European Parliament committee have been trying to probe some of the claims.
'No right to hide'
The International Committee of the Red Cross (ICRC) is the only independent organisation which has been granted access to suspects in US jails in Iraq, Afghanistan and Guantanamo Bay in Cuba.
CIA flights carrying prisoners are suspected of landing in Europe
Mr Kellenberger met US Secretary of State Condoleezza Rice and Defence Secretary Donald Rumsfeld on Friday to press them to allow access to all detainees of the war on terror, an issue the ICRC says was first raised with US authorities two years ago.
In a strongly worded statement following the meeting, the ICRC said the US had moved no closer to permitting access to prisoners in undisclosed locations.
"No matter how legitimate the grounds for detention, there exists no right to conceal a person's whereabouts or to deny that he or she is being detained," Mr Kellenberger said.
He said the ICRC would continue to push for access.
The Geneva Conventions says the ICRC should be allowed to visit prisoners-of-war.
However, the US calls its detainees "enemy combatants" and are not covered by Geneva.
It insists that in practice, however, the vast majority of detainees are allowed to meet the ICRC.
Mr Kellenberger said in the statement that the ICRC would continue to seek access to these people "as a matter of priority" despite the "the disappointing lack of results and the current US position".