Special Correspondent NEW YORK - A secret US memorandum authorised the lethal targeting of radical cleric Anwar al-Awlaki, an American citizen who was killed by a US drone strike last week, The New York Times reported on Sunday. Citing sources who had read the document, the Times said Awlaki, who lived in Virginia before leaving the US shortly after Sept 11, 2001, was the first American citizen who the White House authorised US agencies to kill since the Al Qaeda attacks on New York and Washington a decade ago. Legal experts who have long criticised a US government programme to kill members of Al Qaeda abroad as a breach of international law say the killing of Awlaki last month may also have broken US law. The fact that (Awlaki) was a dual US-Yemeni citizen means that he had extra protections under the US constitution than he would not have had if he was just a Yemeni citizen, said Mary Ellen OConnell, an international law professor at the University of Notre Dames law school. So the president has done something in my view that is highly questionable under our own constitution. The 50-page memorandum completed in June 2010 reportedly justified the operation despite an executive order banning assassinations and international laws prohibiting such activity. The document was tailored specifically to the case of Awlaki and did not seek to set a precedent for similar such operations, according to the report. Awlaki was a legal target for assassination because he was part of Al Qaedas war against the US, he posed a significant threat to US citizens and Yemeni authorities were not taking steps to or were unable to bring him to justice, the document purportedly found. Awlaki, identified by US intelligence as chief of external operations for Al Qaeda in the Arabian Peninsula (AQAP), was killed in a CIA drone attack in a remote Yemeni town last month. He had been implicated in a botched attempt by AQAP to bomb a US-bound plane in 2009 and had contacts with a US Army psychiatrist who killed 13 people at a US military base the same year. US authorities had branded him a global terrorist and last year authorised his capture or killing, but Sanaa had previously appeared reluctant to act against him. Awlaki was eloquent in English and Arabic. US President Barack Obama said last month that the killing in Yemen of Awlaki was another significant milestone in efforts to defeat Al Qaeda and its allies. This is further proof that Al Qaeda and its affiliates will have no safe haven anywhere in the world, Obama said, adding that Awlakis death was a result of the government of Yemen joining international efforts against the militants.