By Phil Stewart and Idrees Ali WASHINGTON (Reuters) - The U.S. military might monitor a North Korean intercontinental ballistic missile test and gather intelligence rather than destroy it, as long as the launch did not pose a threat, Defense Secretary Ash Carter said on Tuesday. North Korea declared on Sunday it could test-launch an ICBM at any time from any location set by leader Kim Jong Un, saying a hostile U.S. policy was to blame for its arms development. If it's not threatening, we won't necessarily do so," Carter said in his final news briefing before President Barack Obama's administration