Updated

The Justice Department has opened an internal investigation into whether its top officials improperly authorized or reviewed the CIA's use of waterboarding when interrogating terror suspects, according to documents released Friday.

The investigation was revealed at the request of Democratic Sens. Dick Durbin of Illinois and Sheldon Whitehouse of Rhode Island. A Justice Department spokesman, however, said the inquiry has been ongoing for several years.

Questions about waterboarding are part of a larger Justice probe of the so-called Bybee memo, wrote Marshall Jarrett, head of the department's Office of Professional Responsibility, in a Feb. 18 letter to the two senators.

"Among other issues, we are examining whether the legal advice contained in those memoranda was consistent with the professional standards that apply to Department of Justice attorneys," Jarrett wrote.

Asked for details, Justice spokesman Brian Roehrkasse said, "This is not a new investigation, but rather has been ongoing for some time."

Waterboarding involves strapping a person down and pouring water over his or her cloth-covered face to create the sensation of drowning. It has been traced back hundreds of years, to the Spanish Inquisition, and is condemned by nations around the world. Critics call it a form of torture.

The memo at the heart of the internal Justice inquiry was dated Aug. 1, 2002, and written by then-Assistant Attorney General Jay Bybee for then-White House Counsel Alberto Gonzales. It defined torture as recognized by U.S. law as covering "only extreme acts" causing pain similar in intensity to that caused by death or organ failure.

The Bush administration maintains waterboarding was legal when it was used by CIA interrogators in 2002 and 2003 on top al-Qaida detainees Khalid Sheikh Mohammed, Abu Zubaydah and Abd al-Rahim al-Nashiri. Earlier this month, CIA Director Michael Hayden said waterboarding was used, in part, because of widespread belief among U.S. intelligence officials that more catastrophic attacks were imminent.

The CIA banned its personnel from using waterboarding in 2006. Attorney General Michael Mukasey has refused to publicly discuss whether waterboarding is currently legal since it is no longer used by CIA interrogators.

Durbin called the internal Justice inquiry "long overdue" and noted that the U.S. government has previously prosecuted waterboarding as a war crime.

"Within the question how America could come to use interrogation techniques of the Inquisition is the question how the Department of Justice could have overlooked its own precedents to authorize waterboarding," added Whitehouse, a former federal prosecutor.

He suggested "the answer was preordained and the department was driven by politics and obedience, not law and independence."

Mukasey told Congress earlier this month that he would not pursue criminal charges against CIA officials who used waterboarding after relying on Justice Department guidance that the interrogation tactic was legal. He said Friday he did not believe the Bybee memo was politically motivated.

"I have no reason to believe that politics was involved in that or any other analysis," Mukasey said.