WASHINGTON: The White House has defended drone strikes on al-Qaeda suspects, including Americans, as legal, ethical and wise, and says they comply with US law and the constitution.
But Pakistan's ambassador to Washington, Sherry Rehman, said US drone strikes in Pakistan were a ''direct violation of our sovereignty'', illegal and counterproductive, producing more militants than they eliminate.
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The increase of US drone attacks against al-Qaeda cells in Yemen has angered residents who say the pilotless craft are killing civilians.
The White House defended President Barack Obama's power to wage drone war after a hitherto secret Justice Department white paper argued Americans high up in al-Qaeda could be lawfully killed, even if intelligence failed to show them plotting an attack.
The disclosure by NBC News came as US drone attacks face increasing scrutiny and questions from human rights groups.
''We conduct those strikes because they are necessary to mitigate ongoing actual threats, to stop plots, to prevent future attacks and, again, save American lives,'' the White House spokesman Jay Carney said on Tuesday.
''These strikes are legal, they are ethical, and they are wise.''
Mr Obama promised in May 2009 that whenever his administration could not release information for national security reasons, he would ''insist that there is oversight of my actions - by Congress or by the courts''.
Senators led by Ron Wyden, a Democrat, have pressed the administration to explain its basis for using lethal force against Americans abroad and renewed their request in a letter this week. ''What the white paper does not do is answer specific questions regarding the scope of the authority and the threshold for evidence of terrorist activity,'' Senator Mark Udall said.
Among the most controversial of the attacks were the September 2011 killings in Yemen of Anwar al-Awlaki and Samir Khan, which stoked concern because they were US citizens never charged with a crime.
The white paper offers a more expansive definition of self-defence and imminent attack than those given publicly in the past by US officials, who have cited ''the inherent right to self-defence'' in defending the attacks.
''The condition that an operational leader present an 'imminent' threat of violent attack against the United States does not require the United States to have clear evidence that a specific attack on US persons and interests will take place in the immediate future,'' it says.
Instead, an ''informed, high-level'' official could decide the targeted individual posed ''an imminent threat of violent attack against the United States'' if he had ''recently'' engaged in such activities, and there was no evidence he had renounced them.
These strikes are legal, they are ethical, and they are wise.
The leak comes just two days before White House counter-terrorism chief John Brennan, a central player in the US drone campaign, goes before the Senate for hearings on his nomination to be head of the CIA. The senators implied in their letter that foot-dragging might hurt Mr Brennan's confirmation.
Agence France-Presse, Bloomberg