A U.N. investigator has called on the Obama administration to justify its policy of assassinating rather than capturing al Qaeda or Taliban suspects, increasingly with the use of unmanned drone aircraft that also take civilian lives. Christof Heyns, U.N. special rapporteur on extrajudicial, summary or arbitrary executions, urged Washington to clarify the basis under international law of the policy, in a report issued overnight to the United Nations Human Rights Council. The U.S. military has conducted drone attacks in Afghanistan, Iraq, Pakistan, Somalia and Yemen, in addition to conventional raids and air strikes, according to Heyns, a South African jurist serving in the independent post. Citing figures from the Pakistan Human Rights Commission, he said U.S. drone strikes killed at least 957 people in Pakistan in 2010 alone. Thousands have been killed in 300 drone strikes there since 2004, 20 percent of whom are believed to be civilians. Although figures vary widely with regard to drone attack estimates, all studies concur on one important point: there has been a dramatic increase in their use over the past three years," Heyns said. Human rights law requires that every effort be made to arrest a suspect, in line with the "principles of necessity and proportionality on the use of force", the investigator said.