WASHINGTON (CNN) -- The Obama administration publicly justified its use of unmanned drones to target suspected terrorists overseas for the first time Monday, with a top official saying the strikes are conducted "in full accordance with the law."
John Brennan, President Barack Obama's top counterrorism adviser said strikes are used when the option of capture is not feasible. Brennan discussed the strikes during a Monday address at the Woodrow Wilson Center, a Washington think-tank.
"President Obama said here five years ago, if another nation cannot or will not take action, we will," Brennan said. "And it is an unfortunate fact that to save many innocent lives we are sometimes obliged to take lives -- the lives of terrorists who seek to murder our fellow citizens."
The program utilizes unmanned aerial vehicles, often equipped with Hellfire missiles, to target al Qaeda operatives in remote locations overseas -- often on the territory of U.S. allies such as Pakistan and Yemen. Brennan said the United States "respects national sovereignty and international law" and is guided by the laws of war in ordering those attacks.
But the attacks have drawn repeated condemnations from Pakistan, which says the strikes have killed numerous civilians. A drone strike hit a high school in the country's northwestern tribal region where intelligence officials said Islamic militants were hiding Sunday, bringing a fresh denunciation from Pakistan's Ministry of Foreign Affairs.
And domestic critics insist that the program isn't legal, and they remain concerned about the targeted killing of Americans like accused al Qaeda leader Anwar al-Awlaki, who died in a drone strike in Yemen in September.
"Mr. Brennan supplies legal conclusions, not legal analysis," said Jameel Jaffer, deputy legal director of the American Civil Liberties Union. "We continue to believe that the administration should release the Justice Department memos underlying the program -- particularly the memo that authorizes the extrajudicial killing of American terrorism suspects. And the administration should release the evidence it relied on to conclude that an American citizen, Anwar al-Awlaki, could be killed without charge, trial, or judicial process of any kind."
And a woman stood up in the middle of Brennan's speech to protest the use of the drone strikes. She was carried out by security.
Brennan's remarks are the Obama administration's most candid and open confirmation of the program to date. Attorney General Eric Holder defended the killing of al-Awlaki in March, saying the United States had the right to use "technologically advanced weapons" against terrorists, and Brennan said the top lawyers for the Pentagon, State Department and CIA have laid out the legal basis for the attacks.
"When considering lethal force, we are of course mindful that there are important checks on our ability to act unilaterally in foreign territories," he said. "We do not use force whenever we want, wherever we want. International legal principles, including respect for a state's sovereignty and the laws of war, impose constraints. The United States of America respects national sovereignty and international law."
Brennan said people are targeted if they are believed to pose a significant threat to the United States or its overseas interests. The targets are usually people holding high-ranking positions within al Qaeda, or who possess critical skills that help enable the terrorist organization to carry out attacks, and there is no feasible chance to capture them.
Arguments in favor of the method include the fact that no U.S. troops are put at risk, and that the precision targeting capabilities enable for the careful avoidance of civilian deaths. Brennan acknowledged that innocent civilians are killed sometimes, and the administration conducts a full review of the operation when that happens.
But he did not address the issue of backlash from al Qaeda or other organizations. In 2009, a CIA base in Afghanistan was targeted by a suicide bomber who posed as a double agent and killed seven CIA Officers along with a Jordanian intelligence official. A Taliban commander claimed that the attack was in retaliation for a drone strike.
And he said the program is now spreading beyond the United States, saying that other countries have the technology -- casting light for the first time on the administration's concerns about the possibility that other countries using this technology against the United States.
"President Obama and those of us on his national security team are very mindful that as our nation uses this technology, we are establishing precedents that other nations may follow," he said. "And not all of them will be nations that share our interests or the premium we put on protecting human life, including innocent civilians."
Brennan also revealed that there are disagreements over use of the program within the administration -- but he added that the nation is at war.
"If anyone in government who works in this area tells you they haven't struggled with this, then they haven't spent much time thinking about it. I know I have, and I will continue to struggle with it as long as I remain involved in counterterrorism."