South Korean media said Mr Kim went there with his sister Kim Yo Jong and other top deputies.
North Korea's leader Kim Jong-un and US President Donald Trump.
"This is not the fault of either Trump or Kim, but rather a reflection that intractable, decades-long strategic challenges rarely-if ever-get resolved in single encounters", Haas writes. Flanked by bodyguards, Kim also visited the Marina Bay Sands resort.
Kim is hoping Trump will relieve the economic sanctions that have crippled the North Korean economy.
Mr Pompeo added that the U.S. was prepared to take action to provide North Korea with "sufficient certainty" that denuclearisation "is not something that ends badly for them".
President Donald Trump will leave Singapore Tuesday night after his historic summit with North Korean leader Kim Jong-un the White House said Monday, adding that talks between USA and North Korean officials "are ongoing and have moved more quickly than expected".
Sanctions will remain until North Korea completely and verifiably eliminates its weapons of mass destruction programs, added Pompeo. "If diplomacy does not move in the right direction. those measures will increase". He had earlier been scheduled to leave on Wednesday.
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A White House read-out of Trump's meetings with Prime Minister Lee Hsien Loong today did not include mention of a state visit. She said their belief is that it occurred "because South Korea attacked them, which is not true". "Now we have this meeting".
Trump also said he would not withdraw US troops from South Korea as part of the agreement, though he would like to "get our soldiers home" at some point.
Another shot shows him atop the hotel, owned by staunch Trump-loyalist Sheldon Adelson, taking in the views night-time views of Singapore's cityscape.
The North Korean delegation is staying at the five-star St. Regis hotel where the lobby has a cream-colored marble floor, chandeliers and large art works on the walls.
Less than a year ago, Trump was threatening "fire and fury" against Kim, who in turn scorned the American president as a "mentally deranged USA dotard".
"We have a very interesting meeting in particular tomorrow (Tuesday), and I think things can work out very nicely", Trump said.
But it was only Monday morning in North Korea that the government news agency reported that Mr Kim was in Singapore, had met Prime Minister Lee Hsien Loong and would meet Mr Trump on Tuesday.
Trump also tweeted: "Meetings between staffs and representatives are going well and quickly. but in the end, that doesn't matter".
- Trump and Kim will start their historic summit at Sentosa Island with a one-on-one session with translators. The hotel has been surrounded by a tight security presence Monday, but pedestrians have been allowed to pass by the hotel, with some peering in to see what's going on.
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Some people were grumbling in the wealthy city-state because of traffic jams caused by the summit and the cost of hosting two leaders with massive security needs. Abbreviating the meeting to a single day could make it easier to cast the summit as an early, symbolic opening, rather than a substantive negotiation in which a lack of tangible progress would suggest failure on the part of the negotiators.
Pompeo has not said if Trump would consider withdrawing almost 28,000 USA troops from the Korean Peninsula.
However, economic sanctions are not likely to be lifted immediately after the summit, U.S. analysts noted, as the process is contingent upon how faithful North Korea is with denuclearization pledge.
Experts believe the North is close to being able to target the entire United States mainland with its nuclear-armed missiles, and while there's deep scepticism that Kim will quickly give up those weapons, there is also some hope that diplomacy can replace the animosity between the USA and the North.
Kelsey Davenport, director for Nonproliferation Policy at the Arms Control Association, said there were signs that the gaps between the two sides were narrowing.
Asked by a reporter how he felt about the summit, Trump said: "Very good". "The process could be doomed before it begins".
Shortly after a group of suited North Korean diplomats set out from their Singapore hotel on Monday for talks with USA officials on the eve of a historic summit, a bigger group of North Koreans headed out in summery shirts for some shopping.
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