四名美国公民死于无人机袭击The US attorney general has acknowledged four US citizens have been killed in drone strikes since 2011.美国司法部长承认，2011 年以来已有四名美国公民死于无人机袭击。 In a letter to the Senate judiciary committee, Eric Holder defended the targeted killing of Anwar al-Awlaki. But he said Awlaki's 16-year-old son as well as two other individuals were "not specifically targeted by the US". The disclosure comes as President Barack Obama prepares to make a speech on counter-terrorism and the drone programme on Thursday. A White House official quoted by Reuters said the US president would discuss why the use of drones was "necessary, legal and just". The disclosure of the killings in Yemen and Pakistan marks the first formal public acknowledgement of the US citizen deaths in drone strikes. "The president has directed me to disclose certain information that until now has been properly classified," Mr Holder wrote. 'Continuing threat' America's top law enforcement official defended the killing of Awlaki, whom he described as a "senior operational leader" of al-Qaeda in the Arabian Peninsula (AQAP). Mr Holder said Awlaki was "intimately involved in detailed planning and putting in place plots against US persons". Mr Holder added officials "appropriately concluded that [Awlaki] posed a continuing and imminent（迫近的） threat" to the US. Awlaki, who was born in the US state of New Mexico, was killed in a missile strike from an unmanned plane in Yemen in September 2011. US officials announced his death but did not officially reveal he was killed by a drone. Samir Khan, a naturalised US citizen who produced an online magazine promoting al-Qaeda's ideology, died in the same missile strike. Awlaki's 16-year-old son Abdulrahman, who was born in Colorado, was killed in Yemen a month later. Jude Kenan Mohammad, a North Carolina resident with a Pakistani father and an American-born mother, was arrested in Pakistan in 2008 after trying to enter a part of the country that is dominated by militants and is off-limits to foreigners. He was charged with weapons possession an d lacking the correct paperwork but disappeared after being granted bail. According to his acquaintances, Mohammad is thought to have died in a strike in November 2011 in Pakistan's South Waziristan region, the New York Times reported.
