European governments face mounting pressure to come clean over their involvement in secret CIA prisons after their existence was acknowledged by the US.
So far all European countries have denied hosting illegal, US-run detention centres for terror suspects.
But Terry Davis, secretary general of the 46-nation Council of Europe, said: "It is in everyone's interests to clear the air. I am not going to accuse governments of lying but clearly it is difficult to reconcile what the Americans have said with what European governments have said."
When the original allegations surfaced last year, Poland and Romania were identified as host countries though both denied involvement. One other possible "black site" is Camp Bondsteel in Kosovo, which human rights monitors have waited two years to inspect.
The US Secretary of State, Condoleezza Rice, made it clear America had acted with the agreement of governments in Europe.
Mr Davis called for a new committee to help monitor the implementation of international agreements to protect human rights.
A German MEP, Wolfgang Kreissl-Doerfler, said: "The location of these prison camps must be made public."Reuse content