The US policy of using aerial drones to carry out targeted killings presents a major challenge to the system of international law that has endured since the second world war, a United Nations investigator has said. Christof Heyns, the UN special rapporteur on extrajudicial killings, summary or arbitrary executions, told a conference in Geneva that President Obama's attacks in Pakistan, Yemen and elsewhere, carried out by the CIA, would encourage other states to flout long-established human rights standards. In his strongest critique so far of drone strikes, Heyns suggested some may even constitute "war crimes". His comments come amid rising...