In a major policy speech, President Obama defended his administration’s use of drone strikes Thursday while also urging Congress to take steps to close the Guantanamo Bay detention center.

Speaking at National Defense University in Washington, D.C., the president acknowledged that drone strikes have killed innocent civilians, but said the targeted military attacks are both legal and effective. Obama said drone attacks have helped disrupt terrorist plots.

“Simply put, these strikes have saved lives,” the president said during this major national security speech. “Moreover, American’s actions are legal. We were attacked on 9/11. Within a week, Congress overwhelmingly authorized the use of force.”

Obama conceded that although the strikes are legal and effective, it doesn’t mean using drones is “wise or moral in every instance.”

The president said he doesn’t authorize drone strikes if U.S. forces or a partnering government are able to capture a suspected terrorist. He called the use of drones “constrained.”

He also acknowledged and apologized for drones that have killed innocent civilians, but said the tragedies have to be weighed against the alternatives.

“It is a hard fact that U.S. strikes have resulted in civilian casualties -- a risk that exists in every war. For the families of those civilians, no words or legal construct can justify their loss,” Obama said. “These deaths will haunt us as long as we live.”

But Obama said that standing idly by isn’t a sufficient strategy, either.

“To do nothing in the face of terrorist networks would invite far more civilian casualties” in places like Yemen, Afghanistan and Somalia, where al Qaeda and its affiliates thrive. “Remember that the terrorists we are after target civilians. So doing nothing is not an option.”

In making his case for drone strikes, Obama argued that conventional attacks are less precise than drones, and said it is “false to assert that putting boots on the ground” means less civilian deaths and military casualties.

“We are choosing the course of action least likely to cause the loss of innocent life,” the president said. “The very precision of drone strikes … can end up shielding our government from the public scrutiny that a troop deployment invites.”

Obama defended the targeted 2011 drone strike that killed U.S. citizen Anwar al-Awlaki in Yemen. Al-Awlaki, a native of New Mexico, was a higher-up in al Qaeda’s Yemeni operations.

“For the record, I do not believe it would be constitutional for the government to target any U.S. citizen with a drone or with a shotgun without due process,” the president prefaced his remarks by saying, in a nod to U.S. Sen. Rand Paul, R-Ky., who filibustered on the issue earlier this year.

In al-Awlaki’s case, Obama said the al Qaeda figure was using his U.S. citizenship “as a shield.”

“When a citizen goes abroad to wage war against American and is actively plotting to kill U.S. citizens” then the use of a drone is appropriate, the president said.

The U.S. government would have preferred to capture al-Awlaki and give him a trial, Obama said, but that was not possible.

“I would have been derelict in my duty had I not authorized the strike that took out Awlaki,” he said.

Turning to Guantanamo Bay, the president signaled his desire to follow through on his campaign promise and close the detention center. He called on Congress to lift detainee transfers from Guantanamo and ordered the Defense Department to designate a site in the U.S. that could hold military commissions.

Obama was greeted with applause after announcing the plan.

"The original premise for opening Gitmo -- that detainees would not be able to challenge their detention -- was found unconstitutional five years ago. In the meantime, Gitmo has become a symbol around the world for an America that flouts the rule of law. Our allies won’t cooperate with us if they think a terrorist will end up at Gitmo. During a time of budget cuts, we spend $150 million each year to imprison 166 people -- almost $1 million per prisoner. And the Department of Defense estimates that we must spend another $200 million to keep Gitmo open at a time when we are cutting investments in education and research here at home and when the pentagon is struggling with sequester and budget cuts," Obama said. “As President, I have tried to close Gitmo. I transferred 67 detainees to other countries before Congress imposed restrictions to effectively prevent us from either transferring detainees to other countries, or imprisoning them in the United States. These restrictions make no sense. After all, under President Bush, some 530 detainees were transferred from Gitmo with Congress’s support. When I ran for president the first time, John McCain supported closing Gitmo -- this is a bi-partisan issue. No person has ever escaped from one of our super-max or military prisons in the United States. Our courts have convicted hundreds of people for terrorism or terrorism-related offenses, including some folks who are more dangerous than most GTMO detainees. There in our prisons. And Given my Administration’s relentless pursuit of al Qaeda’s leadership, there is no justification beyond politics for Congress to prevent us from closing a facility that should have never been opened.”