STORY: Asked during a Pentagon briefing whether he had ruled out an extraterrestrial origin for three airborne objects shot down by U.S. warplanes in as many days, General Glen VanHerck said: "I'll let the intel community and the counterintelligence community figure that out. I haven't ruled out anything.""At this point, we continue to assess every threat or potential threat, unknown, that approaches North America with an attempt to identify it," said VanHerck, head of U.S. North American Aerospace Defense Command (NORAD) and Northern Command.VanHerck's comments after a U.S. F-16 fighter jet shot down an octagonal-shaped object over Lake Huron on the U.S.-Canada border, acting on orders from U.S. President Joe Biden.It was the third unidentified flying object to be knocked out of the sky by U.S. warplanes since Friday, following the Feb. 4 downing of a suspected Chinese surveillance balloon that put North American air defenses on high alert.Another U.S. defense official, speaking on condition of anonymity, said separately after the news briefing that the military had seen no evidence suggesting that any of the objects in question were of extraterrestrial origin.VanHerck told reporters that the military was unable to immediately determine the means by which any of the three latest objects were kept aloft, the means of their propulsion, or where they were coming from.