Saying military drone strikes are effective and legal, U.S. President Barack Obama defends the use of the unmanned aircraft during a policy speech in Washington.

"Dozens of highly skilled al Qaeda commanders, trainers, bomb makers, and operatives have been taken off the battlefield. Plots have been disrupted that would have targeted international aviation, U.S. transit systems, European cities and our troops in Afghanistan. Simply put, these strikes have saved lives. Moreover, America's actions are legal. We were attacked on 9/11. Within a week, Congress overwhelmingly authorized the use of force. Under domestic law, and international law, the United States is at war with al Qaeda, the Taliban, and their associated forces. 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. So this is a just war - a war waged proportionally, in last resort, and in self-defence.

"Beyond the Afghan theater, we only target al Qaeda and its associated forces. Even then, the use of drones is heavily constrained. America does not take strikes when we have the ability to capture individual terrorists - our preference is always to detain, interrogate, and prosecute them," he said.