SEOUL, South Korea—The powerful sister of North Korean leader Kim Jong Un on Wednesday criticized South Korea’s president and threatened a “complete destruction” of bilateral relations after both of the countries tested ballistic missiles hours apart. The launches of missiles underscored a return of tensions between the rivals at a time when talks aimed at stripping the North Korean regime of its nuclear program are stalled. Kim’s sister, Kim Yo Jong, criticized South Korean President Moon Jae-in for comments he made while observing his country’s missile tests, including its first of a submarine-launched ballistic missile. Moon said South Korea’s growing missile capabilities will serve as a “sure deterrence” against North Korean provocations. The tests came hours after the South Korean and Japanese militaries said North Korea had fired two ballistic missiles into the sea. In a statement carried by state media, Kim berated Moon for describing North Korean weapons demonstrations …