The United States will not fly its Osprey military aircraft again until it confirms their safety, a senior White House official said Thursday. White House national security spokesman John Kirby said the United States will get to the bottom of last week’s fatal crash of an Osprey off the coast of southwestern Japan during a routine exercise. Kirby’s remarks during a press briefing came a day after the U.S. military said it would ground its entire fleet of Ospreys deployed worldwide by the Air Force, Navy and Marine Corps, after finding that the Nov. 29 accident may have been caused by a malfunc…