The Swiss-run International Committee of the Red Cross (ICRC) says it will visit key terrorism suspects transferred from secret CIA jails to Guantanamo Bay.
The news comes after Washington acknowledged on Wednesday the existence of the prisons and said that the 14 men had been sent to the US-run detention centre in Cuba.
The Geneva-based organisation said on Thursday that it had received assurances from the United States that the visit would take place under the usual terms and that it would be able to speak to the prisoners in private.
"[The visit] will be next week," said ICRC spokeswoman Antonella Notari. "We were assured that the terms would be in accordance with our standard practices."
In a televised address, President Bush said the suspects, who include the alleged mastermind of the September 11, 2001 attacks, Khalid Sheikh Mohammed, had been kept in CIA custody. They are expected to face trial.
The 14 men were transferred from the secret prisons to the US military base in Guantanamo Bay, Bush said, just hours after the information was declassified.
Bush said that interrogation techniques used at the prisons were tough, but did not include torture.
The ICRC, which has long been pressing for access to all detainees held in Guantanamo, welcomed the move. But it said it had no information on where the 14 had previously been held.
"It is a good sign to transfer them out of undisclosed places of detention," Notari said. "It is a good first step.
Washington's surprise announcement on Wednesday follows previous refusals to admit the existence of secret CIA prisons.
The detention programme, which was revealed by the media last year, prompted an international outcry.
Swiss senator Dick Marty is currently in charge of a European investigation into the matter.
He said that Bush's admission was "just one piece of the truth", but had not come as a surprise to him. "There is more, much more to be revealed by the United States."
The ICRC, which visits prisoners of war under the Geneva Conventions on warfare, always demands access to all detainees and to the facilities where they are held, Notari said.
It insists on meeting each prisoner in private and being able to make repeat visits and relay messages between the prisoners and their families.
Notari said the ICRC had yet to determine whether it has visited the detainees in other locations before their transfer to Guantanamo, "but we don't think so because the information is that they're coming from undisclosed places of detention".
She said ICRC delegates visit detainees in Guantanamo every four to six weeks as a rule and the agency is satisfied with the access they have there.
swissinfo with agencies
In November 2005 the alleged existence of secret detention camps in Europe and the kidnapping of suspected terrorists by the CIA came to light.
The human rights watchdog, the Council of Europe, asked Dick Marty, a Swiss senator and chairman of the council's Committee on Legal Affairs and Human Rights, to launch an investigation.
Marty presented a report in June which accuses 14 European countries of having colluded with the CIA on secret prisons and transfers of terrorism suspects.
The report accuses the Swiss government of turning a blind eye to allegations of suspect aircraft transiting the country's airspace. Switzerland has also extended permission to the end of this year for overflights by non-commercial US aircraft.