Condoleezza Rice has rejected outright allegations that the US is using European airports to transport terror suspects to countries where they might face torture.
The US secretary of state was speaking ahead of a five-day trip to Europe, amid allegations that CIA planes transporting suspects to terror camps, stopping in EU airports to refuel.
"The US does not permit, condone or tolerate torture," she said, adding: "The US does not transport and has not transported detainees from one country to another for the purpose of torture.
"It has not transported anyone to a country where we believe he will be tortured and where appropriate we seek assurances that he will not be tortured."
Press reports claimed that CIA planes have landed in several countries, including Britain and Germany, reportedly on their way to secret camps where torture is carried out.
A number of countries have launched internal investigation into the claims, while foreign secretary Jack Straw has written to Washington on behalf of the EU demanding clarification.
Speaking at Andrews Air Force Base in Maryland, Ms Rice did not deny the existence of the 'hidden' prisons, and admitted that it used a process called rendition to transport terror suspects around the world.
She said such a measure was a "vital tool in combating transnational terrorism" and added that its use is not unique to the US, nor was it unique to the Bush administration.
"The US and those countries will use every lawful measure to protect these citizens," she said, adding that "sometimes, these efforts are misunderstood".
But the secretary of state was adamant that such transporting of suspected terrorists did not lead to them being tortured.
"Acts of physical or mental torture are expressly forbidden. Torture and conspiracy to commit torture are crimes in US law no matter where they occur around the world," she insisted.
In a statement afterwards, Mr Straw welcomed Ms Rice's comments, saying: "All European countries fully share the determination expressed here by the US to protect our citizens from the threat of terrorism, clearly while operating within international law and our treaty obligations.
"Secretary Rice's reply makes clear that US policy is to comply with the UN convention against torture and, in this respect the United States government complies with its constitution, its laws, and its treaty obligations."
Ms Rice will fly to Germany today and is also is scheduled to hold talks in Romania, Ukraine and Belgium.