The New America Foundation's Peter Bergen, who has co-authored a study on U.S. drone attacks, said they are the least bad option that exists because the U.S. military cannot invade the Pakistani tribal areas where many of the militants are based.
Bergen, who also is CNN's national security analyst, said there was tremendous pushback from the Pakistanis when U.S. special forces crossed the border during the previous Bush administration.
"Drone attacks are really the only tool in the toolkit that is possible," Bergen said.