US uses Tony Blair defence to justify drone killings The committees are investigating the drone campaign, which was only recently acknowledged in public by senior US officials. The targeting of American citizens, who have constitutional rights to a fair trial of criminal charges, has provoked particular criticism from human rights campaigners. The memo sets out a three-part test for strikes against US citizens. This dictates that a suspect must pose an "imminent" threat, that his capture must be "infeasible," and that the strike conform to "law of war principles." In what is likely to be one of its most contentious passages, however, the memo makes an expansive case for what constitutes such an "imminent" threat against America, at one stage citing Lord Goldsmith's 2004 comments. "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," the memo states. Before his death Awlaki, who was born in the US and educated at several of its universities, was linked to numerous terror plots, including Umar Farouk Abdulmutallab, the so-called "pants bomber" who attempted to bring down an airliner bound for Detroit on Christmas Day 2009. The document is said to "closely mirror" arguments in secret memos on the drone campaign that were reportedly drawn up for Mr Obama by the office of legal counsel, which gives authoritative legal advice to the president. The administration has not publicly acknowledged that the memos exist. The targeted killing programme is believed to have killed up to 3,000 people. John Brennan, Mr Obama's nominee for CIA director and the architect of the campaign, is expected to face questions about it during a Senate confirmation hearing on Thursday. Lord Goldsmith gave Mr Blair legal approval for British involvement in the war on Iraq days before troops invaded in March 2003. Documents published in 2010 disclosed that he had previously warned Mr Blair that he did not believe the war would be legal, but subsequently changed his mind.