The White House refused to confirm or deny Wednesday that the CIA operates secret prisons, known as "black sites," for Al-Qaeda suspects in eastern Europe and other countries around the world.
The Washington Post reported that the prisons are, or have been, located in eight countries including Thailand, Afghanistan and "several democracies in Eastern Europe" since the system was set up after the September 11, 2001 attacks.
The names of the Eastern European countries were withheld by the Post "at the request of senior US officials," who argued that the disclosure might disrupt counter-terrorism efforts. Thailand denied there was a prison there.
"I am not going to discuss any specific intelligence activities," White House spokesman Scott McClellan said. "I would say that the president's most important responsibility is to protect the American people."
The refusal to discuss the matter was echoed by US Attorney General Alberto Gonzales and the Central Intelligence Agency.
But former president Jimmy Carter denounced what he said was "a profound and radical change in the basic policies or moral values of our country" in reaction to the report.
"This is just one indication of what has been done under this administration to change the policies that have persisted all the way through our history," said Carter, who championed human rights during his 1977-81 presidency.
The existence of secret CIA detention centres has long been claimed. Amnesty International denounced the "archipelago" of prisons in June as a "gulag of our times".
But the report that former Eastern European countries were among the locations is new.
Czech Interior Minister Frantisek Bublan was quoted by the on-line news outlet Aktualne.cz as saying that the Czech Republic recently turned down a US request to set up a detention centre on its territory.
"The negotiations took place around a month ago," he was quoted as saying. The Americans "made an effort to install some of the sort here, but they did not succeed."
Separately, Hungary's intelligence chief, Andras Toth, told AFP that Budapest had not been approached.
"The mere suggestion of this is absurd," Toth said, adding "I know of no such request" from US officials.
The Central Intelligence Agency has sent more than 100 suspects to the hidden global internment network, the Post said, indicating that the number was a rough estimate and did not include prisoners picked up from Iraq.
About 30 of the detainees, considered major terrorism suspects, have been held at "black sites" organised by the CIA in Eastern Europe and elsewhere, it said.
Locations in Thailand and at Guantanamo Bay, Cuba were closed in 2003 and 2004, the daily said. Another in Afghanistan, known as the "Salt Pit" was moved inside Bagram Air Base.
Over 70 other detainees -- with less direct involvement in alleged terrorism and having limited intelligence value -- have been delivered to intelligence services in Egypt, Jordan, Morocco, Afghanistan and other countries, the daily added.
The CIA and the White House have dissuaded Congress from asking questions in open testimony about the facilities, the paper said.
"Virtually nothing is known about who is kept in the facilities, what interrogation methods are employed with them, or how decisions are made about whether they should be detained or for how long," The Washington Post said.
The covert prison system is "known only to a handful of officials in the United States and, usually, only to the president and a few top intelligence officers in each host country," said the newspaper, which pieced together the "contours" of the CIA detention program over the past two years.
Conceived after the September 11 attacks on New York and Washington, the covert prison system has been increasingly debated within the CIA, said the daily.
Some CIA officers consider the system unsustainable and believe it diverts the agency from its main espionage mission.
The idea of holding suspects outside the United States, where it is illegal to hold people in isolation and in secret prisons, was not under consideration before September 11, former government officials told the daily.
"The issue of detaining and interrogating people was never, ever discussed," said one former senior CIA intelligence officer. "It was against the culture and they believed information was best gleaned by other means."