The European Union is to investigate allegations the CIA set up secret jails in eastern Europe and elsewhere to interrogate terror suspects.
Human Rights Watch said it has evidence, based on flight logs, that indicate the CIA transported suspects captured in Afghanistan to Poland and Romania. But the two countries - and others in the former Soviet bloc - denied the allegations.
US officials have refused to confirm or deny the claims.
European officials say any such prisons would violate the continent's human rights principles.
The International Committee of the Red Cross is investigating the claims - first reported Wednesday in the Washington Post- that the CIA has been hiding and interrogating some of its most important al-Qaeda captives at Soviet-era compounds.
A Red Cross spokeswoman said the agency asked Washington about the allegations and requested access to the prisons if they exist. The Red Cross, which has exclusive rights to visit terror suspects detained at a US military base at Guantanamo Bay, Cuba, long has been concerned about reports US officials were hiding detainees from the agency.
Europe's top human rights organisation, the Council of Europe, said it would also investigate.
AP