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".

The powerful sister of North Korean leader Kim Jong Un said her country will never see South Korea as a partner for diplomacy

South Korean President Lee Jae Myung pledged to "respect" North Korea's political system and said Seoul would not seek unilateral reunification in a speech to mark Liberation Day.