The United States has defended its treatment of detainees at its military base on Cuba following fierce criticism from the Red Cross.
Guantanamo security is especially tight after recent spy fears
Christophe Girod - the senior Red Cross official in Washington - said it was unacceptable that the detainees should be held indefinitely at Guantanamo Bay without legal safeguards.
But White House spokesman Scott McClellan said they were treated in accordance with the Geneva Conventions - and that America was at war.
The International Committee of the Red Cross is the only organisation outside the US Government with access to the 600 detainees.
Mr Girod's criticism came as a group of American former judges, diplomats and military officers called on the US Supreme Court to examine the legality of holding the foreign nationals for almost two years, without trial, charge or access to lawyers.
US at war
Mr Girod said the ICRC was making the unusually blunt public statement because of a lack of action after previous private contacts with American officials.
"One cannot keep these detainees in this pattern, this situation, indefinitely," he said during a visit to the US naval base where the Taleban and al-Qaeda suspects are being held.
But George Bush's spokesman said the "enemy combatants" were being held for a reason.
United States Navy base in south-eastern Cuba
Leased by Washington since 1903, but not regarded as US territory
Houses more than 600 al-Qaeda and Taleban suspects
Inmates not covered by US constitutional guarantees
"These individuals are terrorists or supporters of terrorism and we are at war on terrorism and the reasons for detaining enemy combatants in the first place is to gather intelligence and make sure that these enemy combatants don't return to help our enemies plot attacks or carry out attacks on the United States," he said.
Washington says the alleged fighters will get a fair legal hearing in due course.
Mr Girod led a team from the ICRC which has just completed an inspection tour of the detention camp in Cuba.
Although he did not criticise any physical conditions at the camp, he said that it was intolerable that the complex was used as "an investigation centre, not a detention centre".
"The open-endedness of the situation and its impact on the mental health of the population has become a major problem," he told the New York Times.
Christine Huskey, an American lawyer representing 28 Kuwaiti inmates, told the BBC she had had "absolutely" no access to them.
"I represent a ghost," she said.
Mental health problems
In the past 18 months, 21 detainees have made 32 suicide attempts, and many more are being treated for depression, the New York Times says.
Mr Girod says prisoners who spoke to his team regularly asked about what was going to happen to them.
"It's always the number one question," he said. "They don't know about the future."
Camp officials have said most of the detainees' mental health problems existed before they arrived.
The ICRC says it has been urging the White House for months to make significant changes in Guantanamo.
The administration, Mr Girod said, should consider establishing a policy of giving detainees some idea of when they can learn whether they will be charged or released.