Allegations that the CIA abducted and illegally transported terror suspects across European borders are credible, an investigator has said.
Dick Marty has urged the US to confirm or deny the claims
Swiss senator Dick Marty has submitted a report on the claims, made in the media, to a meeting of the human rights committee of the Council of Europe.
Mr Marty criticised the US for refusing to confirm or deny the allegations.
US Secretary of State Condoleezza Rice has repeated assurances that the US would never condone torture.
Speaking in Washington, she made no direct reference to European concerns about the secret CIA flights, but said the US would respect its own laws while recognising that the "war on terror" was a different kind of war.
She said that the US should do anything that was legal to prevent terrorist attacks.
Mr Marty's findings were released in an official statement by a committee of the 46-member Council of Europe, the continent's human rights watchdog.
"The elements we have gathered so far tend to reinforce the credibility of the allegations concerning the transport and temporary detention of detainees - outside all judicial procedure - in European countries," he said.
He went on: "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."
The BBC's Alix Kroeger in Strasbourg says the strongly worded report will add to the pressure for more in-depth inquiries.
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
The European Union has so far declined to investigate, although it has said any member state with secret prisons on its territory could have its EU voting rights suspended.
Poland and Romania have been named by the media as possible locations of CIA secret prisons, but have denied the allegations.
In his statement, Mr Marty said it was "still too early to assert that there had been any involvement or complicity of member states in illegal actions".
But, he warned, if the allegations proved correct any European states involved "would stand accused of having seriously breached their human rights obligations to the Council of Europe".
However, Mr Marty told a news conference he believed any prisoners held secretly by the US in Europe had now been moved to North Africa.
Tony Lloyd, a member of the Council's parliamentary assembly, told the BBC the charges that people may have been effectively kidnapped and taken to other countries for possible torture "were of such magnitude that they have to have proper answers".
Mr Marty urged the US to comment formally on the allegations, saying he "deplore[d] the fact that no information or explanations" were given during last week's tour of Europe by US Secretary of State Condoleezza Rice.
At the time, Ms Rice refused to address claims the CIA operated secret prisons abroad, where suspects could be interrogated without reference to international law.
Condoleezza Rice faced questions over the claims while in Europe
She said American interrogators were bound by a UN treaty banning the use of torture, regardless of whether they were working in the US or abroad.
A group of British MPs investigating the matter, the All Party Parliamentary Group on Extraordinary Rendition, said the UK could have risked breaching its legal obligations.
International law expert Professor James Crawford, of Cambridge University, told the group the UK government must satisfy itself on the issue of torture rather than relying on US assurances.