But Swiss senator Dick Marty said that there was no formal proof so far of the existence of clandestine detention centers in Romania or Poland as alleged by the New York-based Human Rights Watch.
"There is a great deal of coherent, convergent evidence pointing to the existence of a system of "relocation" or "outsourcing" of torture," Marty said in a report presented to the Council of Europe, the human rights watchdog on whose behalf he is investigating.
"Acts of torture or severe violation of detainees' dignity through the administration of inhuman or degrading treatment are carried outside national territory and beyond the authority of national intelligence services."
The report said more than 100 terror suspects may have been transferred to countries where they faced torture or ill treatment in recent years.
"The entire continent is involved," Marty told the Council of Europe's parliamentary assembly, a body comprising several hundred national parliamentarians. "It is highly unlikely that European governments, or at least their intelligence services, were unaware."
In the report, Marty analyzed the cases of an Egyptian cleric allegedly kidnapped from Milan, Italy, in 2003 by CIA agents and a German captured in Macedonia and taken to Afghanistan in an apparent case of mistaken identity.
Citing an American lawyer, Marty also said six Bosnians were abducted by American agents on Bosnian soil and taken to Guantanamo Bay, despite a Bosnia judgment ordering their release.
Last week, Italy's justice minister formally asked the United States to allow Italian prosecutors to question 22 purported CIA operatives they accuse of kidnapping the Egyptian cleric, Osama Moustafa Hassan Nasr, in 2003 from a Milan street.
Nasr, believed to belong to an Islamic terror group, was seized on Feb. 17, 2003. Prosecutors claim the cleric, who is also known as Abu Omar, was taken by the CIA to a joint U.S.-Italian air base, flown to Germany and then to Egypt, where he says he was tortured.
Marty also said he would follow up on evidence gathered in the case of Khaled al Masri, a German of Lebanese origin reportedly kidnapped from Germany to Afghanistan, in the next stage of his investigation.
The Council of Europe launched its probe after allegations surfaced in November that U.S. agents interrogated key al Qaeda suspects at clandestine prisons in eastern Europe and transported some suspects to other countries passing through Europe.
Human Rights Watch identified Romania and Poland as possible sites of secret U.S.-run detention facilities. Both countries have denied involvement. Clandestine detention centers would violate European human rights treaties.
Marty told the parliamentary assembly he obtained on Monday flight logs archived by the Brussels-based air safety organization Eurocontrol so he could determine flight patterns of several dozen suspected CIA planes. Experts say flight logs could help to determine whether the CIA secretly transported prisoners to Europe.
Marty also obtained satellite images of air bases in Romania and Poland, requested by the Council of Europe for analysis after the bases were identified by Human Rights Watch as possible locations of secret detention centers.
But Marty's report — based on his own findings, national investigations and press reports from recent weeks — said there was no formal, irrefutable evidence of the existence of secret CIA prisons in Romania, Poland or any other country.
"On the other hand, it has been proved that individuals have been abducted, deprived of their liberty and all rights and transported to different destinations in Europe, to be handed over to countries in which they have suffered degrading treatment and torture," Marty said, adding that if eventually uncovered, the detention centers would likely be very small cells that would be easily hidden.
Marty complained that there was enormous pressure on him to come up with evidence of secret CIA prisons but not much help was coming from the Council of Europe or governments.
"Not a single day passes without me being asked, 'Do you have any hard evidence, is there any proof?"' he said. "I am not a judicial authority, I have no means of investigation, the logistical support available to me is very limited.