A leaked US government document sets out a legal justification for President Barack Obama's policy of extrajudicial killing, as the United Nations prepares its own investigation into drone strikes. Obama's policy of using lethal force against suspected terrorists is coming under further scrutiny after a Justice Department white paper was obtained by the US media. The document moves the goalposts in regards to when the government is authorised to carry out the killing of a US citizen. This comes as, last week, the UN announced a major investigation into drone strikes. Led by the UN's special rapporteur on counterterrorism and human rights, the study will examine the extent of civilian casualties, and the wider consequences of an expanding global drone war.