Canadian Prime Minister Justin Trudeau called the downing of an aerial object over Yukon in western Canada "a very serious situation," as recovery efforts continued Monday.Trudeau spoke to reporters in Whitehorse and said his government is deploying "all measures possible to keep Canadians safe." "When these unidentified objects represent a threat to airline traffic, to civilian safety, we needed to take action, which we did," Trudeau said. "We did it in concert with our American partners under the command of NORAD," he said. "This is an ongoing effort that will continue as necessary to be able to recover and analyze this object," he said. North American Aerospace Defense Command, the combined U.S.-Canada organization that provides shared defense of airspace over the two nations, detected the object flying at a high-altitude Friday evening over Alaska, U.S. officials said. It crossed into Canadian airspace on Saturday.