WASHINGTON - US President Barack Obama on Thursday sought to define his administration's counterterrorism policies, announcing new guidelines codifying controversial drone strikes against militant targets, while renewing his pledge to close Guantanamo Bay military detention facility.

Obama made the announcement during a major policy speech delivered at the National Defense University. He said he has signed a Presidential Policy Guidance to codify guidelines, oversight and accountability of drone strikes.

He also called on Congress to lift the restrictions on detainee transfers from Guantanamo, while asking the Department of Defense to designate a site in the United States to hold military commissions. He also will appoint an envoy to achieve the transfer of detainees to third countries, while lifting the moratorium on detainee transfers to Yemen.

Obama said the change in policy stemmed from the shifting and evolving threat of terrorism to the United States, as al-Qaeda core was on a path to defeat, al-Qaeda affiliates began to emerge, extremists take foothold in countries like Libya and Syria and home-grown radicalized individuals began to pose real threat.