An administration official disclosed the move Wednesday on the eve of a Senate hearing on Obama's nomination of his top White House anti-terror adviser John Brennan to lead the Central Intelligence Agency in his second term.

Some senators had warned they would use Brennan's confirmation as leverage to force the administration to share more information on the legal and constitutional grounds for the US government killing its own citizens.

The disclosure also comes after NBC News published an unclassified Justice Department white paper covering similar ground, reigniting the debate about the killing of estranged Americans who switched sides in the "War on Terror."