Washington - CIA Director-designate John Brennan strongly defended anti-terror attacks by unmanned drones Thursday under close questioning at a protest-disrupted confirmation hearing. On a second controversial topic, he said that after years of reading classified intelligence reports he still does not know if waterboarding has yielded useful information.

Despite what he called a public misimpression, Brennan told the Senate Intelligence Committee that drone strikes are used only against targets planning to carry out attacks to hurt the United States, never as retribution for an earlier one. "Nothing could be further from the truth," he declared.

Referring to one American citizen killed by a drone in Yemen in 2011, he said the man, Anwar al-Alawki, had ties to at least three attacks planned or carried out on U.S. soil. They included the Ft. Hood, Texas, shooting that claimed 13 lives in 2009, a failed attempt to down a Detroit-bound airliner the same year and a thwarted plot to bomb cargo planes in 2010.

"He was intimately involved in activities to kill innocent men women and children, mostly Americans," Brennan said.

In a long afternoon in the witness chair, Brennan declined to say if he believes waterboarding amounts to torture, but he said firmly it is "something that is reprehensible and should never be done again."

Brennan, 57 and President Barack Obama's top anti-terrorism aide, won praise from several members of the committee as the day's proceedings drew to a close, a clear indication that barring an unexpected development, his confirmation as the nation's next head of the CIA is on track. The panel will meet in closed session next week to permit discussion of classified material.

Brennan bristled once during the day, when Sen. James Risch, R-Idaho, accused him of having leaked classified information in a telephone call with former government officials who were preparing to make television appearances.

"I disagree with that vehemently," the nominee shot back.

Brennan is a veteran of more than three decades in intelligence work, and is currently serving as Obama's top counter-terrorism adviser in the White House. Any thought he had of becoming CIA director four years ago vanished amid questions about the role he played at the CIA when the Bush administration approved waterboarding and other forms of "enhanced interrogation" of suspected terrorists.

On the question of waterboarding, Brennan said that while serving as a deputy manager at the CIA during the Bush administration, he was told such interrogation methods produced "valuable information." Now, after reading a 300-page summary of a 6,000-page report on CIA interrogation and detention policies, he said he does "not know what the truth is."

In the hours before the hearing began, Obama ordered that a classified paper outlining the legal rationale for striking at U.S. citizens abroad be made available for members of the House and Senate intelligence panels to read.

It was an attempt to clear the way for Brennan's approval, given hints from some lawmakers that they might hold up confirmation unless they had access to the material.

Sen. Ron Wyden, D-Ore., said he was encouraged when Obama called him on the telephone to inform him of his decision. But he said that when he went to read the material he became concerned the Department of Justice "is not following through" on the presidential commitment. Prodded to look into the matter, Brennan said he would.

Wyden made the drone strikes the main focus of his time to question Brennan, asking at one point what could be done "so that the American people are brought into this debate and have a full understanding of what rules" are for their use.

Brennan said the day's hearings were part of that effort, and he said he backs speeches by officials as a way to explain counter-terrorism programs. He said there is a "misimpression by the American people" who believe drone strikes are aimed at suspects in past attacks. Instead, he said, "we only take such actions as a last resort to save lives" when there is no other alternative in what officials believe is an imminent threat.

Fewer than 50 strikes took place during the Bush administration, while more than 360 strikes have been launched under Obama, according to the website The Long War Journal, which tracks the operations.

Administration officials say Brennan would further limit the use of drones by the CIA and leave the majority of strikes to the military. He signaled in his written answers that he would not seek to expand the CIA's paramilitary operations. In written responses to questions from the committee in advance of the hearing, Brennan wrote, "While the CIA needs to maintain a paramilitary capability ... the CIA should not be used, in my view, to carry out traditional military activities."

The CIA's drone strikes primarily focus on al-Qaida and Taliban targets in the tribal regions of Pakistan. The agency also carries out strikes in Yemen, where three American citizens with al-Qaida connections have been killed: al-Awlaki, his 16-year-old-son and Samir Khan.