A month-old investigation has reinforced allegations the CIA ran a network of secret prisons in Europe, abducted prisoners and transferred them between countries, a European human rights investigator said on Tuesday.
Swiss senator Dick Marty, who is looking into the scandal for the 46-nation Council of Europe human rights watchdog, criticised the United States for failing to come clean over the allegations.
But he said his main mandate was to look into the actions of European states and that it was hard to believe that certain governments and secret services in Europe had not co-operated with the CIA - in breach of their human rights obligations.
Pressure is growing on Washington and European governments to explain dozens of flights criss-crossing the continent by CIA planes, some suspected of delivering prisoners to jails in third countries where they may have been mistreated or tortured.
"Legal proceedings in progress in certain countries seemed to indicate that individuals had been abducted and transferred to other countries without respect for any legal standards," Marty said in a written statement after briefing the Council of Europe's legal affairs and human rights committee in Paris.
"The ... information gathered to date (has) reinforced the credibility of the allegations concerning the transfer and temporary detention of individuals, without any judicial involvement, in European countries."
Marty said in the statement that his findings justified continuing an in-depth inquiry, but he declined to give any details at a news conference.
He urged all member governments to cooperate fully with the investigation, adding that not all - including his home country Switzerland - appeared to be doing so.
The European Union and at least eight member states said last month they were seeking answers from the United States over the use of bases on the continent for secret prisoner transfers, known as "renditions".
The Council of Europe has set governments a three-month deadline to reveal what they know about the mystery flights and about a Washington Post report saying the Central Intelligence Agency ran secret prisons in Eastern Europe.
"I find it hard to believe these actions could have taken place without a degree of collaboration or passivity by governments or services operating under them. I am thinking of the secret services," Marty said.
It was possible, he added, that the secret services had not informed their governments of any co-operation with the CIA.
Marty said the United States had never formally denied the allegations and US Secretary of State Condoleezza Rice had failed to reject them during a recent trip to Europe.
"The rapporteur ... deplores the fact that no information or explanation had been provided on this point by Ms Rice during her visit to Europe," he said.
Human Right Watch, an international watchdog, has named Poland and Romania as two countries where the CIA may have kept prisoners. Poland and Romania have denied the accusations.
Marty said any prisoners held in Europe had now been moved elsewhere by the CIA, including to north Africa.