WASHINGTON (CNN) -- John Brennan told his Senate confirmation hearing on Thursday that he was aware of the CIA's enhanced interrogation techniques while serving as a top official at the agency but did nothing to stop them because he had no oversight role.
"I did not take steps to stop the CIA use of those techniques," said Brennan, who was nominated by President Barack Obama to lead the spy agency after the resignation of former Gen. David Petraeus over an extra-marital affair.
The issue was one of the most controversial in the administration of former President George W. Bush in the aftermath of the September 11, 2001, terrorist attacks.
Brennan's answers to questions about what critics contend was torture acknowledged that he knew another part of the agency was carrying out a directive from the Bush administration.
"I had awareness that the agency was being asked to do it. I was aware that the agency was moving ahead on it," he told the Senate Intelligence Committee, adding that he was not involved in managing it.
Brennan served as the CIA's deputy executive director at the time.
On the same issue, Brennan said a committee report on the interrogation techniques contained "disturbing" information that raised questions in his mind about whether he knew what really happened.
The 6,000-page report took six years to compile, and Brennan said he read the 300-page executive summary before Thursday's hearing.
"Now I have to determine what the truth is. I do not know what the truth is," he said about what he read.
Under persistent questioning by Democratic Sen. Carl Levin of Michigan, Brennan pledged that waterboarding -- or simulated drowning -- would never be used under his direction, but he refused to label it torture.
On another controversial issue -- drone strikes on terrorist targets abroad -- Brennan defended the 2011 killing of Yemeni-American Anwar al-Awlaki as part of the war against al Qaeda.
Brennan said al-Awlaki was involved in efforts to kill Americans, which made him a legitimate military target.
Under prodding by committee chairwoman Sen. Dianne Feinstein, Brennan confirmed a connection between al-Awlaki and Umar Farouk Abdul Mutallab, who tried to detonate an explosive in his underwear on a flight about to land in Detroit on Christmas Day in 2009.
However, Brennan offered no details of the connection, and noted al-Awlaki's role as a propagandist for al-Qaeda who fomented anti-American sentiments via the Internet.
The hearing was temporarily halted at the start when protesters repeatedly interrupted Brennan's opening statement. Some waved signs accusing Brennan of war crimes because of the drone attacks.
Feinstein ordered the room cleared of spectators after a fifth straight person began shouting as Brennan tried to speak. She told security officers to prevent the re-entry of protesters from Code Pink, which describes itself as a women-initiated group for peace and social justice.
Brennan has served as Obama's top counterterrorism adviser and is considered to be behind the administration's dramatic rise in the use of drones against terror suspects.
Several strikes have killed Americans, notably al-Awlaki.
Brennan defended the drone program Thursday, saying that Obama "insisted that any actions we take will be legally grounded, will be thoroughly anchored in intelligence, will have the appropriate review process, approval process before any action is contemplated, including those actions that might involve the use of lethal force."
"My role as the president's counterterrorism adviser was to help to orchestrate this effort over the past four years to ensure, again, that any actions we take fully comport with our law and meet the standards that I think this committee and the American people expect of us as far as taking actions we need to protect the American people, but at the same time ensuring that we do everything possible before we need to resort to lethal force," he said.
An unclassified outline of the administration's policy given to Congress last summer indicated that the government could use lethal force against an American citizen overseas if the person was a senior operational leader of al Qaeda or one of its affiliates and an attack was imminent.
One of the questions the committee submitted to Brennan in advance of the hearing asked how it was determined that an individual was associated with al Qaeda and that a threat was imminent to justify military force. The question did not distinguish between Americans and others.
Brennan responded in writing that related decisions were made on a "case by case basis" as part of a process involving coordination with other agencies.
The White House said this week that questions around the issue have been weighed against legal concerns and discussed publicly.
The Supreme Court has held that the military may constitutionally use force against an American who is a part of enemy forces.
Still civil liberties and other groups want more answers.
Amnesty International weighed in on the debate, saying Congress should grill Brennan on his claim that the Obama administration's drone strikes are "conducted in full compliance with the law."
Other controversies at hand
Brennan's chances to lead the CIA at the start of Obama's first term were scuttled by questions about enhanced interrogations of terror suspects.
At Thursday's hearing, Brennan said he raised objections with colleagues to the enhanced interrogation techniques but denied any role in managing or enabling their use.
Asked if the controversial techniques yielded intelligence that saved lives, Brennan avoided a direct answer but repeated his insistence that such techniques would never happen under his watch.
Senate lawmakers also asked about Brennan's role in administration leaks about covert operations, including a foiled al Qaeda bomb plot in Yemen involving a mole.
He denied any wrongdoing Thursday, saying that he only got involved after leaks became public and that he tried to stem a "hemorrhaging" of leaked information in the matter.
Brennan acknowledged in his written responses to committee questions that he voluntarily was interviewed by prosecutors about those investigations. He said in both cases his counsel told him he was only a witness in those probes, not a target.
A powerful figure at White House
As the president's top counterterrorism aide, Brennan continues to be seen as all-powerful.
"I do think John is regarded in terms of the intelligence community, even where he is now, as the first among equals," CNN national security contributor Frances Fragos Townsend said.
As CIA director, Brennan would report to James Clapper, the director of national intelligence. But when there's a call for highly secretive covert action, he would have a direct path to the president, talking to him on the phone or walking right into the Oval Office to brief him.
By Barbara Starr. Pam Benson and Tom Cohen
CNN's Tom Dunlavey and Lesa Jansen contributed to this report.
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