Senior U.S. officials who authorized and carried out torture as part of former President George W. Bush's national security policy must be prosecuted, a top United Nations special investigator said Wednesday.

Ben Emmerson, the UN's special rapporteur on counterterrorism and human rights, said in addition that all CIA and other U.S. officials who used waterboarding and other torture techniques must be prosecuted.

He said the Senate intelligence committee report on the CIA's harsh interrogation techniques at secret overseas facilities after the 9/11 terror attacks shows "there was a clear policy orchestrated at a high level within the Bush administration, which allowed to commit systematic crimes and gross violations of international human rights law."

The report, released Tuesday, has sparked a firestorm of controversy in the U.S. and abroad. President Barack Obama said the interrogation techniques "did significant damage to America's standing in the world and made it harder to pursue our interests with allies."

"The individuals responsible for the criminal conspiracy ... must be brought to justice, and must face criminal penalties commensurate with the gravity of their crimes," Emmerson said. "The fact that the policies revealed in this report were authorized at a high level within the U.S. government provides no excuse whatsoever. Indeed, it reinforces the need for criminal accountability."

European Union spokeswoman Catherine Ray emphasized that the Obama administration has worked since 2009 to see that torture is not used anymore but said it is "a commitment that should be enshrined in law."

Bush approved the program through a covert finding in 2002 but he wasn't briefed by the CIA on the details until 2006. Obama banned waterboarding and other tactics, yet other aspects of Bush's national security policies remain, most notably the U.S. detention center at Guantanamo Bay, Cuba, and sweeping government surveillance programs.

According to Emmerson, international law prohibits granting immunity to public officials who allow the use of torture, and this applies not just to the actual perpetrators but also to those who plan and authorize it. As a result, he said, the U.S. government is "legally obliged to bring those responsible to justice."

Human Rights Watch's executive director Kenneth Roth also said "unless this important truth-telling process leads to prosecution of officials, torture will remain a `policy option' for future presidents."

Also Wednesday, the head of the CIA during President George W. Bush's second term says "I didn't lie" to Congress about harsh interrogations of terrorism suspects.

Michael Hayden headed the CIA during the second term of George W. Bush's administration. (Chuck France/Associated Press)

Retired Gen. Michael Hayden does say the intelligence community laboured after Sept. 11, 2001 to repel further attacks against the U.S.

Hayden tells NBC's Today show he advocated keeping Congress informed of what the intelligence community was doing. He said his objective "was to get these people to be part of the game."

Asked if Americans have the right to be appalled by the revelations in the Senate intelligence committee report about brutal interrogation tactics like waterboarding, Hayden said he didn't know.

But he added that "it's probably a good thing" the public now knows what efforts the CIA was making on its behalf.