WASHINGTON — The U.S. on Thursday imposed sanctions on a North Korean husband and wife living in Beijing accused of helping to procure equipment for ballistic missiles that ended up in the hands of North Korean and Iranian customers. Treasury’s Office of Foreign Assets Control said Choe Chol Min and his wife Choe Un Jong work through North Korea’s Second Academy of Natural Sciences, a state organization that conducts research for the nation’s ballistics missiles program, to help procure equipment for buyers. Treasury says Choe Chol Min worked with North Korean weapons trading officials to buy equipment for Iranian customers. His wife is accused of coordinating at least one order for dual-use bearings that are used in North Korean ballistic missile production.