The US secretary of state says the UN treaty on torture applies to American interrogators in the US and overseas, in an apparent shift in US policy.
Condoleezza Rice has defended the US policy of "rendition"
The Bush administration has previously said the convention, which bans cruel, inhumane and degrading treatment, does not apply to US personnel abroad.
Correspondents say a reason for the shift might be pressure from Congress.
Condoleezza Rice's European tour has been dogged by claims the CIA used foreign bases to hold terror suspects.
The UN high commissioner for human rights has called on the US to provide information about any secret detention centres and to provide access to them.
Louise Arbour said such detention centres could create conditions where torture might be used, but she welcomed Ms Rice's statement.
Ms Rice said the US was bound by the UN Convention against Torture (CAT).
Germany is one of the countries reported as a CIA landing spot
It "extends to US personnel wherever they are, whether they are in the US or outside the US," Ms Rice said in Ukraine.
Her comments appear to contrast with the US Attorney-General, Alberto Gonzales, who said last year the convention did not apply to US interrogations of foreigners overseas.
US officials travelling with Ms Rice were quoted by Reuters news agency as saying it represented a marked shift in US policy.
But, according to AFP news agency, one aide to Ms Rice said her remarks were "a clarification of policy, not a shift".
The BBC's Justin Webb in Washington says Ms Rice's comments signal an important change in US policy on the use of harsh methods of interrogation - and an apparent softening of the White House position.
The White House has allowed the CIA to use practices such as mock drowning of prisoners, which would almost certainly be considered unacceptable under the terms of the convention, our correspondent says.
Some former detainees have alleged they were part of a US network of "ghost flights" and secret prisons run by the CIA around the world.
They claim they were subjected to beatings, electric shock treatments and solitary confinement during their detention.
Ms Rice has admitted that terror suspects are flown abroad for interrogation under a process called rendition, but denied they were tortured.
She refused to address the claims of secret CIA prisons abroad where suspects could be interrogated without reference to international law.
A number of senior Republicans have been campaigning recently for the White House to be clearer in defining and banning torture.
Claims and denials
Claims that the CIA was holding al-Qaeda suspects in eastern Europe, Thailand and Afghanistan were first reported on 2 November.
New York-based Human Rights Watch said it had evidence that suspects were taken to Poland and Romania.
Both Poland and Thailand on Wednesday reiterated their denials that any secret CIA jails were allowed to operate on their territory. Romania has also dismissed the claims.
Germany, Spain, Sweden and Iceland are all investigating claims that CIA planes landed at their airports while transporting terror suspects.