Germany, Hungary, Italy, Morocco, Norway, Poland, Romania, Spain and Sweden have all been linked to the CIA's use of planes for the transit, or rendition, of prisoners allegedly subjected to extra-judicial detention and torture.
In Olso, the Norwegian government summoned a US embassy official over the landing in Oslo on 20 July of a plane which according to media reports was one of those the CIA used to transport the suspected extremists.
According to a foreign ministry spokesman, the official "denied that the plane in question had been used by the American authorities at the time".
The Swedish government similarly demanded "complete information" from its civil aviation authorities after a news agency reported at least two suspected CIA planes had landed at Swedish airports over the past three years and that one of them was used at the US base in Guantanamo Bay, probably for transporting prisoners.
In Morocco, Le Journal weekly on Saturday cited a former agent with the national DST intelligence service as saying the country had directly participated in the CIA operation with at least ten flights carrying prisoners landing in Morocco between December 2002 and February this year.
In Spain, El Pais cited a report by the civil guard, which has military as well as police functions, as saying the prisoner transport planes made at least 10 secret stopoffs at Palma de Mallorca in the Balearic Islands betwen 22 January, 2004 and 17 January, 2005.
That news prompted Interior Minister Jose Antonio Alonso to say on Tuesday that if the reports were true, it could damage relations between Madrid and Washington as such flights would be "intolerable in every sense".
Spain's United Left opposition party has demanded that Alonso appear before parliament to explain the situation along with Alberto Saiz, head of national intelligence bureau CNI.
CIA called for an inquiry
into the "information leaks"
The US Senate has asked the CIA to inform it as to the precise nature of its prisoner transport operations.
According to the Washington Post, the CIA has placed more than 100 illegally held suspects in a secret prison network in Afghanistan, Thailand and Eastern Europe since the September 11 attacks on the United States.
Following that report the CIA called on the Justice Department to hold an inquiry into the "information leaks" on the prisons.
A series of denials on the existence of the prisons for top al-Qaida suspects has come from Thailand and eastern European US allies, including Bulgaria, Hungary, Poland and Romania.
Only the Czech Republic has gone as far as saying it turned down a US demand to house prisoners previously held at Guantanamo on its soil.
The International Committee of the Red Cross says it has tried in vain for more than two years to persuade Washington to give it access to those held secretly abroad "in the context of the war on terrorism".
An investigation is under way in Germany over the February 2003 kidnap in Italy by CIA agents of Abou Omar, a former imam who was allegedly brought to the US military base at Ramstein in southwestern Germany prior to his being taken to Egypt.
In Italy on Friday, the Milan public prosecutor demanded the extradition of 22 CIA agents believed to have been involved in the abduction of Omar, the subject of an Italian anti-terrorist investigation.
The Italian government has demanded "the full respect of Italian sovereignty" in the affair.
UN special rapporteur into torture, Manfred Nowak, has called on the EU and the European Council to "hold high level inquiries" into the sea of allegations and the European Council says one is to follow.