The nuclear umbrella that the USA has over South Korea, that is meant to protect it from any missile strikes from the North. They blew up a site - which was the real deal site. He added that Otto Warmbier, an American once detained in North Korea, "did not die in vain" because his death brought about the nuclear talks.
Kim was due to leave on Tuesday afternoon, a source involved in the planning of his visit has said.
It however did not give any details on how denuclearisation would be achieved.
The formal document-signing followed a series of meetings at a luxury Singapore resort.
They concluded the meeting with lofty promises by the USA president to take care of a "very risky problem" and Mr Kim forecasting "major change for the world".
Kim Jong Un in turn said: "We overcame all obstacles and came here today".
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Donald Trump and Kim Jong Un exchanged warm words as they came together for a historic nuclear summit that seemed unthinkable months ago.
Trump also tweeted: "Meetings between staffs and representatives are going well and quickly. but in the end, that doesn't matter. Many people in the world will think of this as a scene from a fantasy.science fiction movie". "This is a very, look this is 72 years we're talking about, and we put it into one very intensive day and some meetings beforehand". After the meetings, the two teams and other senior officials met for a working lunch, where beef short ribs, sweet and sour pork and "Daegu Jormin", or Korean braised cod, were served for the main course, according to the menu. He pressed the president on his previous criticism of North Korea's human rights abuses including starving his people, running labor camps and assassinating members of his own family.
Trump spoke only briefly in public on Monday, forecasting a "nice" outcome.
The "Fox and Friends" presenter apologized to viewers after referring to the leaders as "two dictators" ahead of their historic meeting in Singapore Tuesday. But he added "our hostages" are back home and testing, research and launches have stopped.
He would not say whether that included the possibility of withdrawing USA troops from the Korean Peninsula, but said the context of the discussions was "radically different than ever before".
"Nothing to see here, Fox & Friends just casually calling Trump a dictator now", wrote another user. USA officials have said a best case scenario would be that it serves as a launching pad for negotiations that would provide Kim with physical security and his closed off nation with economic assurances in exchange for irreversibly dismantling his country's nuclear capabilities.