North Korea is stepping up criticism of South Korea's new President Lee Jae Myung as he prepares for his first summit with U.S President Donald Trump, calling Lee's efforts to engage with Pyongyang a "pipedream".

North Korean leader Kim Jong Un's sister repeated her dismissal of Seoul's outreach efforts, saying that South Korea "cannot be a diplomatic partner."

SEOUL, South Korea (AP) — North Korean leader Kim Jong Un condemned South Korean-U.S. military drills and vowed a rapid expansion of his nuclear forces to counter rivals, state media said Tuesday, as he inspected his most advanced warship being fitted with nuclear-capable systems.