Obama: 'This is a just war'

In a speech at the National Defense University in Washington, Obama said the U.S. drones program was legal and argued strikes had been effective in fighting extremists who launched the Sept. 11, 2001, terrorist attack.

"We are at war with an organization that right now would kill as many Americans as they could if we did not stop them first," Obama said. "So this is a just war – a war waged proportionally, in last resort, and in self-defense."

But Obama also announced he had approved and declassified a set of guidelines governing the use of drone strikes that would authorize a strike only when there is a “continuing and imminent threat” that other governments cannot address.

Read more on The Hill's DEFCON blog.