A United Nations investigator on Tuesday called on Washington to justify its policy of killing al Qaeda and Taliban suspects, rather than capturing them, at the risk of harming civilians. Christof Heynes urged the U.S. to clarify its basis for using the killings—especially the unmanned drone attacks—under international law. “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,” Heynes said in the 28-page report. The U.S. has conducted drone attacks in Afghanistan, Iraq, Yemen, Saudi Arabia, Somalia, and Pakistan—where drone attacks have been the source of tension between the two countries. The 47-member Human Rights Council will hold a debate on the issue on Tuesday.