The White House has categorically dismissed Pakistan's concerns on the drone strikes, as a top Obama aid describing it as a both 'legal' and 'ethical' tool to get dreaded terrorists.

"As a matter of international law, the United States is in an armed conflict with Al-Qaeda, the Taliban, and associated forces, in response to the 9/11 attacks, and we may also use force consistent with our inherent right of national self-defence," John Brennan, Assistant to the US President for Homeland Security and Counterterrorism said on Monday.

"There is nothing in international law that bans the use of remotely piloted aircraft for this purpose or that prohibits us from using lethal force against our enemies outside of an active battlefield, at least when the country involved consents or is unable or unwilling to take action against the threat," Brennan said in his remarks at the Woodrow Wilson Center, a Washington-based think tank.

Broadly speaking, the debate over strikes targeted at individual members of Al-Qaeda has centered on their legality, their ethics, the wisdom of using them, and the standards by which they are approved, he noted. "These targeted strikes are legal," he asserted.

"To briefly recap, as a matter of domestic law, the Constitution empowers the President to protect the nation from any imminent threat of attack," the US official said.

"The Authorisation for Use of Military Force - the AUMF - passed by Congress after the September 11th attacks authorises the president 'to use all necessary and appropriate force' against those nations, organizations and individuals responsible for 9/11. There is nothing in the AUMF that restricts the use of military force against Al-Qaeda to Afghanistan," he said.

Brennan said the targeted strikes are ethical, adding that it is useful to consider such strikes against the basic principles of the law of war that govern the use of force. Targeted strikes, he argued, conform to the principle of necessity - the requirement that the target have definite military value.

"In this armed conflict, individuals who are part of Al-Qaeda or its associated forces are legitimate military targets. We have the authority to target them with lethal force just as we targeted enemy leaders in past conflicts, such as German and Japanese commanders during World War II," he said.

Targeted strikes conform to the principle of distinction - the idea that only military objectives may be intentionally targeted and that civilians are protected from being intentionally targeted, Brennan said.

"With the unprecedented ability of remotely piloted aircraft to precisely target a military objective while minimising collateral damage, one could argue that never before has there been a weapon that allows us to distinguish more effectively between an Al-Qaeda terrorist and innocent civilians," he said.

Brennan said that targeted strikes conform to the principle of proportionality -- the notion that the anticipated collateral damage of an action cannot be excessive in relation to the anticipated military advantage.

"By targeting an individual terrorist or small numbers of terrorists with ordnance that can be adapted to avoid harming others in the immediate vicinity, it is hard to imagine a tool that can better minimise the risk to civilians than remotely piloted aircraft," the US official said.

For the same reason, he said, targeted strikes conform to the principle of humanity which requires us to use weapons that will not inflict unnecessary suffering.

"For all these reasons, I suggest to you that these targeted strikes against Al-Qaeda terrorists are indeed ethical and just. Of course, even if a tool is legal and ethical, that doesn't necessarily make it appropriate or advisable in a given circumstance. This brings me to my next point," he said.

Targeted strikes are wise as remotely piloted aircraft in particular can be a wise choice because of geography, with their ability to fly hundreds of miles over the most treacherous terrain, strike their targets with astonishing precision, and then return to base, Brennan said.

"They can be a wise choice because they dramatically reduce the danger to US personnel, even eliminating the danger altogether. Yet they are also a wise choice because they dramatically reduce the danger to innocent civilians, especially considered against massive ordinance that can cause injury and death far beyond its intended target," he said.

In addition, compared against other options, a pilot operating this aircraft remotely - with the benefit of technology and with the safety of distance - might actually have a clearer picture of the target and its surroundings, including the presence of innocent civilians, the Obama advisor said.

"There's another reason that targeted strikes can be a wise choice - the strategic consequences that inevitably come with the use of force," he said.

Deployment of large armies abroad also can pose problems as foreign countries typically don't want foreign soldiers in their cities and towns.

In fact, large, intrusive military deployments risk playing into Al-Qaeda's strategy of trying to draw us into long, costly wars that drain us financially, inflame anti-American resentment and inspire the next generation of terrorists, the US official added.