CIA director nominee John Brennan has defended the US drone-strikes programme at a Senate confirmation hearing.
Mr Brennan said the US only took such action as a last resort and was careful to prevent civilian deaths.
The hearing was repeatedly interrupted by protesters as the nominee began to deliver his testimony.
The session comes after lawmakers received secret memos on the rationale for drone strikes on Americans working with al-Qaeda abroad.
Mr Brennan, 57, who is President Barack Obama's top White House counter-terrorism adviser, was a senior CIA official under President George W Bush.
'Significant concerns'
As he began to deliver his prepared remarks on Thursday, he was interrupted several times by protesters, prompting committee chair Senator Dianne Feinstein to order a recess.
We know that that Senate intelligence committee is deeply frustrated at its lack of, well, intelligence. And we know that several senators are very concerned about leaks.
The protestors who interrupted the opening of the hearing served a purpose for John Brennan. They misunderstood, he said, the care we take on the drone programme.
Mr Brennan spoke clearly and often with vigour. Even so, he ducked and weaved at times, leading to the accusation of stonewalling from Senator Ron Wyden. Had "enhanced interrogation" techniques led to the capture of Osama Bin Laden? Back came a long answer that really didn't address the question.
He said "enhanced interrogation", i.e. waterboarding and sleep deprivation, was something that he had objected to in private at the time, though back in 2007 he had said it saved lives. Now, in the light of a Senate Democrats' report, he wasn't so sure.
"At this point, senator," he said, "I don't know what the truth is."
The protestors who interrupted the opening of the hearing served a purpose for John Brennan. They misunderstood, he said, the care we take on the drone programme.
Mr Brennan spoke clearly and often with vigour. Even so, he ducked and weaved at times, leading to the accusation of stonewalling from Senator Ron Wyden. Had "enhanced interrogation" techniques led to the capture of Osama Bin Laden? Back came a long answer that really didn't address the question.
He said "enhanced interrogation", i.e. waterboarding and sleep deprivation, was something that he had objected to in private at the time, though back in 2007 he had said it saved lives. Now, in the light of a Senate Democrats' report, he wasn't so sure.
"At this point, senator," he said, "I don't know what the truth is."
- Read more from Jonny
One of the demonstrators held a sign saying "Brennan = Drone Killing".
During later questions, Mr Brennan said some Americans believe that strikes are used to punish for past transgressions.
"Nothing could be further from the truth," he said. "We only take such actions as a last resort to save lives when there's no other alternative to taking an action that's going to mitigate that threat."
The US has ordered about 350 drone strikes in Pakistan since 2004 - according to data from the Bureau of Investigative Journalism andthe New American Foundation - with the large majority occurring during the Obama administration.
Correspondents say there has been no suggestion that members of the Senate Select Committee on Intelligence object to Mr Brennan's nomination.
He is expected to be confirmed by the panel and later by the full Senate.
When asked about waterboarding, Mr Brennan said it was "reprehensible and should never be done again", but declined several times to say whether it was torture.
"I had expressed my personal objections and views to some agency colleagues," he said during the hearing.
"But I did not try to stop it, because it was something that was being done in a different part of the agency under the authority of others."
He added that during his time at the CIA during the Bush administration, he had been told that waterboarding and other extreme interrogation methods produced "valuable information".
But he said that after reading a 300-page summary of a 6,000-page report on CIA interrogation and detention policies, he did "not know what the truth is".
Drone court?
Mr Brennan's hearing comes a day after the Department of Justice agreed to send Congress documents laying out the legal rationale for targeting and killing US citizens who are suspected of working with terror groups.
The justice department acted after NBC News published a leaked internal memo explaining some of the legal arguments.
White House spokesman Jay Carney said the administration was making an "extraordinary accommodation" in allowing lawmakers to view the secret documents.
The CIA has carried out drone strikes in Yemen, where three American citizens linked to al-Qaeda have been killed: Anwar al-Awlaki, his 16-year-old-son and Samir Khan.
Recent opinion polls have suggested that the US public generally supports the drone programme, especially when compared with the possibility of ground assault.
Ms Feinstein said on Thursday the committee should look into the creation of a special court to evaluate evidence against Americans who might be targeted through drones, similar to the scrutiny applied to eavesdropping on citizens with suspected ties to terrorist groups.
And outgoing defence secretary Leon Panetta, who headed the CIA from 2009 to 2011, told NBC News on Sunday that he favoured shifting most strikes to the military, saying it would make the programme "much more transparent".
Mr Brennan was considered for the top post at the intelligence agency in 2008.
But he withdrew his name from consideration amid questions about the role he played during the CIA's use of waterboarding, viewed by many as torture.
