A senior US official has defended the country's treatment of terror suspects and the transfer of prisoners to third countries for interrogation.
Khaled al-Masri says he was a victim of the US rendition policy
State department senior legal adviser John Bellinger told the BBC Washington sought reassurance in those countries that prisoners would not be tortured.
He said allegations that hundreds of suspects were sent around the globe to be tortured were "ludicrous".
Poland is investigating reports the CIA ran secret jails on its territory.
Prime Minister Kazimierz Marcinkiewicz ordered the investigation saying it was necessary to resolve the issue once and for all.
"This matter must finally be closed, because it could prove dangerous for Poland," he said.
A senior military analyst for the New York-based Human Rights Watch, Marc Garlasco, has said that until recently Poland was the chief CIA detention site in Europe, part of a system of clandestine prisons for interrogating al-Qaeda suspects.
Poland's outgoing President Aleksander Kwasniewski has repeatedly denied such reports.
Human rights activists have accused the US of easing curbs on torture.
US Secretary of State Condoleezza Rice has just returned to Washington after a week-long trip to Europe where she faced questions about treatment of prisoners.
Mr Bellinger said the US did practice rendition, by which some terror suspects were sent to a third country to be questioned.
Ms Arbour said the torture ban was a casualty of the war on terror
But he added that even transferring a prisoner to a country which had been criticised over its human rights record was not a violation of international law.
"We as a state department have got problems with the human rights records of some countries... but this does not mean per se that you may not transfer a person to those countries," he told BBC Radio 4's Today programme.
Mr Bellinger insisted that if there were such questions, the US would seek reassurances that a prisoner would not be subjected to torture.
But he said some practises had been wildly exaggerated.
"Some of the allegations more broadly about all sorts of things are ludicrous, [like one] about hundreds of flights from European cities taking people to be tortured," he said.
He repeated that Washington did not condone or practise torture but would not comment on whether some prisoners had been subjected to interrogation techniques such as waterboarding - when a suspect is made to feel that they are drowning - to extract information.
The lawyer said he could not comment on speculation about so-called enhanced interrogation techniques or the existence of secret prisons.
UN High Commissioner for Human Rights Louise Arbour said on Friday that she believed the US was among a group of countries "advocating an erosion of the total ban on torture".
She said she was "looking forward" to a meeting with Ms Rice, scheduled for January.