U.S. President Barack Obama deliveries a speech at the National Defence University in Washington D.C. on May 23, 2013. Obama on Thursday sought to redefine his administration's counterterrorism policies, announcing new guidelines codifying controversial drone strikes against militant targets, while renewing his pledge to close the Guantanamo Bay military detention facility. (Xinhua/Fang Zhe)

U.S. President Barack Obama deliveries a speech at the National Defence University in Washington D.C. on May 23, 2013. Obama on Thursday sought to redefine his administration's counterterrorism policies, announcing new guidelines codifying controversial drone strikes against militant targets, while renewing his pledge to close the Guantanamo Bay military detention facility. (Xinhua/Fang Zhe)

U.S. President Barack Obama deliveries a speech at the National Defence University in Washington D.C. on May 23, 2013. Obama on Thursday sought to redefine his administration's counterterrorism policies, announcing new guidelines codifying controversial drone strikes against militant targets, while renewing his pledge to close the Guantanamo Bay military detention facility. (Xinhua/Fang Zhe)

U.S. President Barack Obama deliveries a speech at the National Defence University in Washington D.C. on May 23, 2013. Obama on Thursday sought to redefine his administration's counterterrorism policies, announcing new guidelines codifying controversial drone strikes against militant targets, while renewing his pledge to close the Guantanamo Bay military detention facility. (Xinhua/Fang Zhe)

U.S. President Barack Obama deliveries a speech at the National Defence University in Washington D.C. on May 23, 2013. Obama on Thursday sought to redefine his administration's counterterrorism policies, announcing new guidelines codifying controversial drone strikes against militant targets, while renewing his pledge to close the Guantanamo Bay military detention facility. (Xinhua/Fang Zhe)