Fourteen European states colluded with the CIA in secret US flights for terror suspects, a report concludes.
CIA flights have landed in European countries, Mr Marty says
The report comes from Europe's human rights watchdog, the Council of Europe.
It says there is evidence to back suspicions secret prisons are or were located in Poland and Romania - allegations both countries deny.
Under the CIA policy of rendition, prisoners are moved to third countries for interrogation. There have been allegations some were tortured.
The US admits to picking up terrorism suspects but denies sending them to nations to face torture.
The report by Swiss Senator Dick Marty follows a seven-month inquiry.
It began in November amid a political outcry over media allegations of the existence of CIA detention centres in eastern Europe.
Mr Marty has drawn on air traffic logs, satellite photos and accounts of prisoners who say they were abducted.
In an interim report in January, Mr Marty said European governments were almost certainly aware of the CIA's secret prisoner flights via European airspace or airports.
The new report says: "It is now clear - although we are still far from having established the truth - that authorities in several European countries actively participated with the CIA in these unlawful activities.
"Other countries ignored them knowingly, or did not want to know."
Spain, Turkey, Germany and Cyprus provided "staging posts" for rendition operations, while the UK, Portugal, Ireland and Greece were "stop-off points", the report says.
It says Italy, Sweden, Macedonia and Bosnia allowed the abduction of residents from their soil.
The most serious charges are levelled at Poland and Romania, where Mr Marty says there is enough evidence to support suspicions that CIA secret prisons were established.
Although the Swiss senator says the US must bear responsibility for the flights, he says the programme could operate only with "the intentional or grossly negligent collusion of the European partners".
The "spider's web" of US rendition flights is based on an "utterly alien" approach that breaches human rights, he concludes.
In Warsaw, Polish Prime Minister Kazimierz Marcinkiewicz described the latest accusations as "libellous", while Romania rejected them as "speculation".
COUNCIL OF EUROPE
Founded in 1949 and based in Strasbourg, France
Forty-six members, 21 of them from Central and Eastern Europe
Set up to defend human rights, parliamentary democracy and the rule of law
Acts as human rights watchdog for Europe
Oversees the European Court of Human Rights
Comprises a decision-making committee of ministers and 630-member parliamentary assembly
In London, Tony Blair said the report "added absolutely nothing new whatever to the information we have".
The BBC's Security correspondent, Frank Gardner, says that while the report makes uncomfortable reading for many European countries, the Council of Europe has been hampered by its lack of investigative powers.
The evidence in the report is largely circumstantial, our correspondent says, and proving many of the allegations, such as the existence of so-called "black sites", is beyond the Council's powers.
The report is intended to wake up Europe's conscience to get national parliaments to investigate properly, our correspondent concludes.
Media allegations on CIA jails broke last November, when the Washington Post newspaper said the intelligence agency had been running facilities in eastern Europe, Afghanistan and Thailand.
It said more than 100 people had been sent to facilities known as "black sites" since they were set up following the 11 September 2001 attacks.
European media reports have since alleged that the CIA has used several European airports for its programme of "extraordinary renditions".
Under the highly secretive process, US intelligence agencies send terror suspects for interrogation by security officials in other countries, where they have no legal protection or rights under American law.
Washington does not deny that terror suspects have been transferred for interrogation in other countries, but rejects accusations that they are being tortured.