The American administration has been quick to accuse these groups of being a front for al-Qaeda, thereby justifying the use of drones to attack them.

ECONOMIST: Yemen's turmoil

The debate over the use of attack drones will no doubt continue, even as U.S. troops continue to draw down in places like Afghanistan, reducing the number of combatants apt to encounter militants face-to-face.

CNN: Dronestagram uses social media to highlight drone strikes

Sen Paul said Mr Holder's responses in that hearing had come close to assuring him the government would not attack Americans with drones in the US, but he said he was "alarmed" by the difficulty of getting the White House to define clearly what qualified as a legitimate target.

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