Human rights commissioner Alvaro Gil-Robles said he had been “shocked” by conditions at the barbed wire-rimmed centre inside a US military base, which he witnessed in 2002.
The camp resembled “a smaller version of Guantanamo”, he told France’s Le Monde newspaper, referring to the US centre at Guantanamo Bay, Cuba, where hundreds of terrorism suspects remain detained without trial.
Mr Gil-Robles told the daily he had inspected the centre, located within the US military’s Camp Bondsteel in Kosovo, in 2002, to investigate reports of extrajudicial arrests by NATO-led peacekeepers.
He described seeing “small wooden huts ringed by tall barbed wire”, each housing “between 15 and 20 prisoners … wearing orange boiler-suits like the ones worn by Guantanamo inmates”.
Some prisoners were bearded and reading the Koran, he added.
Washington has faced severe criticism from human rights groups for keeping suspects in the US war on terrorism that was launched after the September 11, 2001 attacks locked up at Guantanamo Bay without access to lawyers, some for years.
More recently, it has also been accused of maintaining a network of so-called “black sites” — covert CIA detention centres in foreign countries, notably in Asia and in eastern Europe — where suspects are subjected to vigorous interrogation techniques some critics say amount to torture.
Mr Gil-Robles said he had no evidence that Camp Bondsteel was linked to the alleged CIA operations.
“But I do believe that an explanation should be given for this base in Kosovo, as for other potentially suspect sites” in Europe, he told the paper.
Earlier this week the Council of Europe, which guarantees human rights in its 46 member states, launched an investigation into the alleged prisons.
The official leading the probe said today Romania, which rights groups have labelled a likely site for one of the secret centres, was not hosting a large, Guantanamo-style jail.
Dick Marty told a press conference in Bucharest he was “convinced that there are no Guantanamos in Romania”.
“I don’t think it would be possible to set up a centre like Guantanamo in Europe,” said Marty. “If Romanian officials tell me they are not hosting a Guantanamo, I trust them.”
However, he did not exclude the possibility of Romania having “small centres with one or two detainees being kept temporarily for interrogation”.
“It’s also possible that CIA planes stay 10, 20 or 30 days on Romanian soil. That’s very hard to find out,” he added.
Claims about the alleged prisons, as well as reports of covert CIA flights carrying prisoners from country to country, have prompted rights groups and a number of politicians around Europe to demand their governments press the United States for answers.
British Foreign Secretary Jack Straw, whose country holds the rotating European Union presidency, said on Tuesday he would be asking Washington for an explanation of the affair.