FILE – In this Jan. 31, 2010 file photo, an unmanned U.S. Predator drone flies over Kandahar Air Field, southern Afghanistan, on a moon-lit night. A U.N. expert on Friday, Oct. 18, 2013 called on the United States to reveal the number of civilians it believes have been killed by American drone strikes targeting Islamic militants. U.N. Special Rapporteur Ben Emmerson said that preliminary information gathered for a new report indicated more than 450 civilians may have been killed by drone strikes in Pakistan, Afghanistan and Yemen, but more work needs to be done to confirm the figures.(AP Photo/Kirsty Wigglesworth, File)