When Mukasey took the same stance last October it briefly threatened to derail his confirmation as attorney general until he assured Democrats in the senate that he would review the legality of the controversial interrogation tactic and report back.

But before the US senate judiciary committee today, Mukasey said he would not rule on whether it was a form of illegal torture because it was not part of the current interrogation methods used by the CIA on terror suspects.

He said current interrogation methods were lawful.

"Given that waterboarding is not part of the current programme, and may never be added to the programme, I do not think it would be appropriate for me to pass definitive judgment on the technique's legality," he said.

The Democratic chairman of the committee, Patrick Leahy, accused Mukasey of ducking questions.

It is not enough to say that waterboarding is not currently authorised," said Leahy. "Torture and illegality have no place in America."

Leahy accused President Bush's administration of having "twisted America's role, law and values" so that officials were "instructed by the White House not to say that waterboarding is torture and illegal". Waterboarding involves strapping a person down and pouring water over his cloth-covered face to create the sensation of drowning.

The CIA and the Pentagon banned waterboarding in 2006 but critics want the justice department to join other nations in outlawing the practice.

However, US intelligence officials fear that doing so could make government interrogators - including those from the CIA - vulnerable to retroactive criminal charges or civil lawsuits.

Waterboarding is at the heart of a justice department criminal inquiry over whether the CIA illegally or otherwise improperly destroyed videotapes in 2005 of two terror suspects being interrogated.

The tapes showed harsh interrogations - possibly including waterboarding - of suspected terrorists Abu Zubaydah and Abd al-Rahim al-Nashiri in 2002, when both suspects were held in secret CIA jails overseas.

The tapes were destroyed as intelligence officials debated whether waterboarding should be declared illegal.