North Korea appeared close Sunday to test-firing a long-range missile capable of reaching the United States, prompting the White House to warn of an appropriate response and Japan to threaten a "fierce" protest to the United Nations. North Korea was silent on the issue but vowed to bolster its "military deterrent" in a burst of fiery rhetoric carried by its state news agency. A test launch of what is believed to be a Taepodong-2 missile would inflame a region already tense over the North's continuing nuclear weapons program. "There are signs" of an imminent missile launch, Jung Tae-ho, a spokesman at the South Korean president's office, told The Associated Press. He added that security officials were "closely watching the situation."