CIA chief defends 'lawful' interrogation

“The best sources of information on terrorists and their plans are the terrorists themselves.”

Hayden said: "The irreplaceable nature of that intelligence is the sole reason we have rendition, detention and interrogation programmes."

Several senior Senate Democrats had vowed to vote against the president’s nominee for attorney general, Michael Mukasey, unless he stated unequivocally that the practice of “waterboarding” was torture. That would render the technique, already forbidden by the US military, illegal.

In September ABC News reported that Hayden had banned waterboarding in CIA interrogations in 2006. Agency officials have neither confirmed nor denied waterboarding prisoners in the past, and they would not confirm the reported ban.

After his remarks in Chicago, an audience member asked Hayden: “Is waterboarding torture and will you continue to waterboard? Yes or no.”

In his answer, Hayden briefly discussed constitutional law, the United Nations Convention Against Torture and the Geneva Convention, before ending: “Judge Mukasey cannot nor can I answer your question in the abstract. I need to understand the totality of the circumstances in which this question is being posed before I can give you an answer.”

It is believed that fewer than five high-value detainees have been subjected to waterboarding and the technique has not been used since 2003.

Waterboarding simulates drowning by immobilising a prisoner with his head lower than his feet and pouring water over his face.

Hayden said harsher interrogation techniques were used in “small, carefully run operations” that had been applied to fewer than 35 prisoners since 2002.

In a letter to Senate Judiciary Committee Democrats, Mukasey called waterboarding “repugnant” but said he did not know if it was illegal because he had not been cleared to receive a classified briefing on it.

If after further study he found that it was, he would rescind any federal legal opinion that allowed its use, he wrote.