The news comes hours before Trump is set to become the first sitting US president to meet with a North Korean leader.
Kim Yong-chol worked in North Korean intelligence for 30 years and is now in charge of relations with South Korea and the United States.
The relative speed with which state media reported on Kim's arrival suggests a some confidence that the meeting will go well - or at least well enough.
The historic first meeting between a sitting USA president and and North Korea's leader will take place Tuesday at 9 a.m. when Trump and Kin will meet alone with only translators in the room.
The two leaders will first meet face to face with only translators present before being joined by other officials from both nations for an expanded meeting and working lunch.
The tour came approximately 12 hours ahead of Kim's summit with U.S. President Donald Trump at Singapore's secluded Sentosa Island. Trump later accused the New York Times of quoting a senior White House official "who doesn't exist".
He said the U.S. would be satisfied with nothing less than the complete, verifiable and irreversible denuclearisation of the Korean peninsula - with verification the key part of any deal.
Kim smiled as he took a selfie with Singapore's Foreign Minister Vivian Balakrishnan at the scenic waterfront Gardens by the Bay.
The US was prepared to offer certainty to North Korea so it could be "comfortable that denuclearisation isn't something that ends badly for them".
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"I'm very optimistic that we will have a successful outcome from our meetings tomorrow", he said.
South Korean President Moon Jae-in, right, gestures as he speaks to Kim Yo-jong, the sister to North Korean leader Kim Jong-un.
"The ultimate objective we seek with diplomacy with North Korea has not changed", Pompeo said.
Gorka also said that he was "very disappointed" in Canadian Prime Minister Justin Trudeau following his remarks after the G7 Summit over the weekend. Trump had previously said the talks might extend beyond the first day.
What's more, the official U.S. "memorandum of conversation", or "MemCom", of that meeting was written by the longtime U.S. Russian-to-English interpreter Dmitri Zarechnak, according to a copy of the document posted by the National Security Archive at The George Washington University.
In fact, North Korea merely said it would suspend nuclear and missile tests and shut down a key testing site.
The relationship between the US and its allies was already off-balance after Mr. Trump just a week before the summit imposed 25% tariffs on steel and 10% tariffs on aluminum from the European Union and Canada.
Trump told reporters the Singapore summit is "really a get-to-know-you kind of situation".
"It's unknown territory in the truest sense but I really feel confident", Trump said.
Kim is expected to stay at the St Regis hotel and Trump at the Shangri-La, both in the Tanglin area in downtown Singapore.
The North has faced crippling diplomatic and economic sanctions as it has advanced development of its nuclear and ballistic missile programs.