The UN's human rights chief has said US military drone attacks in Pakistan raise serious legal questions.
Navi Pillay was speaking at the end of a fact-finding visit to Pakistan.
Drone attacks have become a central part of US counter-terror operations but Pillay said they were legally problematic.
US officials defended the policy after al-Qaeda leader Abu Yahya al-Libi was reportedly killed in a drone strike earlier this week.
US Defence Secretary Leon Panetta said that the US would "continue to defend ourselves".
Pillay also voiced concerns that the strikes were being conducted "beyond effective and transparent mechanisms of civilian or military control".
She also suggested to the Pakistani government that they invite the United Nations Special Rapporteur on Summary or Arbitrary Executions to investigate some of the incidents.