AP
U.S. Vice President Mike Pence addresses members of U.S. military services and Japan Self-Defense Force before he departs for South Korea, at U.S. Air Force Yokota base in Fussa, on the outskirts of Tokyo, Japan, Thursday, Feb. 8, 2018. (Toru Hanai/Pool Photo via AP)
South Korean army's armored vehicles move during a military exercise in Paju, South Korea, near the border with North Korea, Wednesday, Feb. 7, 2018. Vice President Mike Pence said the U.S. is preparing to announce the "toughest and most aggressive" economic sanctions against North Korea in the coming days, boosting pressure on the bellicose government during the Winter Olympics. (AP Photo/Ahn Young-joon)
FILE - This 2015, file photo provided by the North Korean government shows North Korean leader Kim Jong Un and his sister Kim Yo Jong, left, during their visit to a military unit in North Korea. South Korea’s Unification Ministry said North Korea informed Wednesday, Feb. 7, 2018, that Kim Yo Jong would be part of the high-level delegation coming to the South for the Pyeongchang Winter Olympics. Independent journalists were not given access to cover the event depicted in this image distributed by the North Korean government. The content of this image is as provided and cannot be independently verified. (Korean Central News Agency/Korea News Service via AP, File)