WASHINGTON - President Barack Obama's nominee to be CIA director strongly defended anti-terror attacks by unmanned drones Thursday under close questioning at a protest-disrupted Senate confirmation hearing.John Brennan, who has been a prime architect of drone operations under President Obama, also faced questions about a decade of CIA mistakes and misdeeds, from abuse of detainees to leaks of classified information.The highly unusual public hearing cast a rare spotlight on a spy agency that operates in the shadows. Senators from both parties took turns pushing John Brennan for his views of covert programmes that have garnered headlines, including the administration's expanded use of targeted killings by drone aircraft, a highly classified effort he helped design and oversee as White House counter-terrorism chief.Brennan's confirmation is all but assured. But the sharp questions reflected deep frustration on the part of the Senate Intelligence Committee, which has battled the Obama administration over access to classified documents, and which has not held a single public hearing on CIA drone strikes that have killed an estimated 3,000 suspected militants in Pakistan, Yemen and Somalia in the last four years.Brennan claimed that the administration's drone strike programme is legal, carefully managed and important to national security. "We only take such actions as a last resort to save lives," he told the Senate Intelligence Committee.The security issues that have dominated the country's national security debate over the past decade played out in the hearing room. Brennan was asked about waterboarding, lethal drone strikes and upheaval in the Middle East.The confirmation hearing was delayed by protesters against drone strikes and other counterterrorism policies . Senator Dianne Feinstein, a Democrat, who chairs the intelligence committee, ordered the hearing room cleared before Brennan, who is closely associated with drone strikes, could complete his opening statement.Brennan told the committee that critics, such as the protesters, are unaware of "the care that we take and the agony that we could go through" to try to avoid civilian casualties. Feinstein claimed the number of civilian casualties caused by drone strikes are in the single digits yearly.Lawmakers expressed concerns about oversight of the drone strikes. Sen. Ron Wyden, a Democrat, told Brennan the Obama administration has "stonewalled" the committee and others on information about the drone program, saying, "Every American citizen has the right to know when the government thinks it has a right to kill them."The killing of US-born cleric Anwar al-Awlaki in a drone strike in Yemen in 2011 raised concerns among civil rights advocates and lawmakers about the precedent of targeting an American citizen.In an attempt to boost Brennan's nomination and quell congressional critics, Obama directed the Justice Department to provide the Senate and House intelligence committees with Office of Legal Counsel advice related to the administration's drone policy.The release came hours before the confirmation hearing. Wyden accused the Justice Department of not following through on the president's pledge to provide all the legal justifications and said he wanted access to the documents before voting on the nomination.Brennan expressed some skepticism about the idea of establishing a court-like system to approve drone strikes, saying that protecting American lives is "inherently an executive branch function."Feinstein has speculated about bringing some more oversight and transparency to the system. "We need to look at the whole process and figure a way to make it transparent and identifiable," Feinstein said after the hearing.Brennan, a CIA official during the George W. Bush administration, found himself answering questions about the "enhanced interrogation techniques" used during those years against terrorist suspects. Brennan said he registered "personal objections" to waterboarding, a practice critics have called torture, but had no authority to stop it."Waterboarding is reprehensible and should not be used," Brennan said, though he declined to say whether he personally regards it as torture. "I am not a lawyer and cannot address that question," he said.The nominee said he did not know whether enhanced interrogation techniques led to the raid that killed 9/11 architect Osama bin Laden. "I do not know what the truth is," Brennan said.A veteran employee of the CIA , Brennan identified a number of challenges facing the agency: upheaval in the Middle East; continued struggles against al-Qaeda terrorists; cyber-attacks from other countries, criminals and terror groups; and efforts by Iran and North Korea to pursue nuclear weapons and missiles to deliver them.Brennan pledged to keep intelligence committee members in the loop on CIA operations, saying there would be no "trust deficit."Brennan criticized news leaks of classified information. "These leaks damage our national security, sometimes gravely, putting these CIA employees at risk and making their missions more difficult," Brennan said.Feinstein praised the nominee , saying, "John Brennan, by all accounts, will be a strong leader" of the CIA .James Carafano, a foreign policy analyst at the conservative Heritage Foundation, said there is much to criticize in Obama and Brennan's counterterrorism policies , but he doesn't see "enough heat to stop confirmation" in a Democratic-controlled Senate.If confirmed, Brennan would replace David Petraeus, who resigned from the CIA in November after revelation of an extra-marital affair.During the hearing, Brennan said Awlaki had an operational role in al-Qaeda in the Arabian Peninsula. Feinstein asked Brennan a series of questions aimed at drawing out more information about Awlaki and his role in terrorist plots against the United States.At the end of the three-and-a-half-hour hearing, Feinstein complimented Brennan for what she called his forthright and direct responses to questions, giving him a strong endorsement. "I think you are going to be a fine and strong leader of the CIA ," she told him.