Trump and Kim are set to meet in Vietnam for their second summit in an effort to thaw relations between the former foes and reduce one of the world's biggest nuclear threats.
Veteran North Korean diplomats are being sidelined from nuclear talks ahead of a second summit with the United States as recent defections and allegations of spying undermine the trust of leader Kim Jong Un, South Korean officials and experts say.
"Nothing is agreed to until everything is agreed to", one official said.
On a chair next to him, nine-year-old To Gia Huy emerges as a spitting image of a miniature Kim Jong Un. "I really like Donald Trump, so I want to have (his) hairstyle", he said.
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He said Moscow hoped the Vietnam summit would end with a positive result but added: "You can not expect to solve it at a two-day meeting, this is a long road". "This is an important step towards that ultimate goal", the official said.
The administration has pointed to the release of hostages held in North Korea, although that took place before the summit, and the repatriation of a fraction of US remains from the Korean War.
Asked whether Trump was open to withdrawing all US troops from the Korean peninsula for a peace treaty that would formally end the war, a second official said that was "not the subject of discussions".
And there are serious implications for South Korea's security, it added.
The U.S. has been demanding that North Korea give up a nuclear weapons program that threatens the United States.