US drone strikes: Memo reveals case for killing Americans 5 February 2013 Last updated at 11:15 The legal basis for using drone strikes to kill US citizens has been disclosed in a leaked justice department memo. US officials can authorise the killing of Americans abroad if they are leaders of al-Qaeda or its allies, according to the document obtained by NBC News. Lethal force is lawful if they are judged to pose an "imminent threat" and their capture is not feasible, it adds. US drone strikes against militant suspects in countries such as Yemen and Pakistan are deeply controversial. Under President Barack Obama the US has expanded its use of drones to kill hundreds of al-Qaeda suspects, arguing that it is acting in self-defence in accordance with international law. Critics argue the drone strikes amount to execution without trial and cause many civilian casualties. Among those killed was US citizen Anwar al-Awlaki, an al-Qaeda suspect who died in a drone strike in Yemen in September 2011. Legal framework The undated 16-page Department of Justice White Paper published by NBC gives more details of the justification for the use of drones outside recognised war zones. It says sovereignty is not deemed to have been violated if the host nation gives its consent, or is unwilling or unable to suppress the threat posed by the individual targeted. It also sets out a "legal framework" for the use of lethal force against US citizens in foreign countries. It concludes that such killings do not violate the US Constitution as long as: An informed, high-level official of the US government has determined that the targeted individual poses an imminent threat of violent attack against the US Capture is infeasible and the US continues to monitor whether capture becomes feasible The operation would be conducted in a manner consistent with applicable law of war principles The paper adopts a broad definition of "imminent threat," saying it is not necessary to produce evidence that a specific attack is being planned if the target is generally engaged in plotting against the US. It also asserts that courts should not play a role in reviewing or controlling such decisions. The Obama administration has been under growing pressure from politicians in Congress to share more details of its drone strike programme, including secret legal documents. Last month the UN launched an inquiry into the impact of drone strikes on civilians.