President Obama's nominee to head the CIA on Thursday defended America's use of killer drone strikes abroad to a Senate panel, saying they are ordered only as a last resort to protect lives when there is no other way to capture a suspected terrorist.

In a nearly four-hour hearing before the Senate Select Intelligence Committee, John Brennan said the use of unmanned aircraft, which have killed several Americans suspected of plotting terrorist attacks as well as foreign terror suspects and a number of innocent civilians, remains a vital weapon against al Qaeda and other terror groups.

"I believe that there need to be continued speeches that are going to be given by the executive branch to explain our counterterrorism programs," Brennan, who now serves as Obama's top Homeland Security and Counterterrorism adviser, told the panel. "I think there is a misimpression on the part of some American people who believe that we take strikes to punish terrorists for past transgressions. Nothing could be further from the truth."

Brennan made the remarks after Chairwoman Dianne Feinstein, D-Calif., was forced to clear the committee room of protesters determined to interrupt his testimony.

"Stop the killing of Pakistani children!" shouted one man associated with the group Code Pink, as he was escorted from the room by police.

Brennan said the protesters "really have a misunderstanding" of the drone program "and the care that we take and the agony that we go through to make sure that we do not have any collateral injuries or deaths."

Prior to the start of the hearing, the White House delivered to lawmakers on the committee the classified legal justification for the use of drone strikes, but some Democrats on the panel were not satisfied with the information.

Feinstein told Brennan that she is seeking more legal documents related to drone strikes and is considering "legislation to ensure that drone strikes are carried out in a manner consistent with our values."

The panel also questioned Brennan about his view of enhanced interrogation techniques, including water boarding, which were used in the past by the CIA to coax information from suspected terrorists.

Brennan said he never supported such techniques but did nothing to stop them because he was not "in the chain of command."

Brennan disputed claims made by his former superior at the CIA that he helped devise the program.

Sen. Saxby Chambliss, R-Ga., then asked Brennan why he had received about 50 emails related to enhanced interrogation techniques.

Brennan again denied involvement.

"I was on thousands upon thousands of email distributions as deputy executive director," he told the panel. "I think I was just CC'ed on them."

Overall, Brennan appeared to handle the committee's concerns, and there is no real threat he will not be confirmed.

Several lawmakers at the hearing showered him with praise as the right person for the job and as someone who might be willing to work more closely with the Intelligence Committee than past CIA directors.

One of the panel's main grievances with the secretive CIA is the agency's reluctance to provide information.

"I quite honestly do not recall anybody who was more forthright, more direct, more accommodating without violating who you are and more open to the possibility of working with this committee," said Sen. Jay Rockefeller, D-W.Va.