Asked about a North Korean state media report that Trump and Kim were set to talk denuclearization and peace on the Korean peninsula, the official said the report is a hopeful indication. It will be the first time a sitting USA president has met with a North Korean leader.
In return, Kim, said to be in his mid-thirties, called Trump "mentally deranged" and a "dotard".
In a statement, the White House said Mr Trump would speak to the media before departing for the United States at 8:00pm.
As he disembarked from Air Force One, Trump told reporters that he feels "very good" about his prospects.
Reunification, he said, would be impossible because four powers - the US, China, Russia and Japan - do not want to see a unified Korea.
The US president has also raised the possibility of further summits and an agreement ending the Korean War by replacing the armistice signed in 1953 with a peace treaty.
Pope to oil execs: Energy needs mustn't destroy civilisation
Fossil fuel firms present at the conference included ExxonMobil, BP, Royal Dutch Shell, Norway's Equinor and Pemex of Mexico. He also said that the world must move toward using clean energy and a reduction in the use of fossil fuels.
Trump expressed optimism about Tuesday's meeting during a working lunch with Singapore's Prime Minister Lee Hsien Loong and aides to both leaders.
He said Iran views Mr Trump and the USA with "great pessimism", saying they are known for "quitting treaties and violating their commitments".
Ferial Saeed, a former State Department official, writes that the summit will be a "getting to know you meeting, "plus.' That means, lower your expectations, and that the president is likely to lean toward keeping his own counsel and eschew a script".
The president has said that he would be willing to guarantee the safety of Kim's regime - though it's not clear how he would back that up.
Kim, on the other hand, has shown he is prepared for his moment on the world stage, and could end up outfoxing Trump, said Victor Cha, a senior adviser and Korea Chair at the Center for Strategic and International Studies in Washington.
Unlike most other publications, USA Today had a different outlook of the Trump-Kim meeting. Just meeting with Trump will also give Kim recognition as the leader of a "normal" country and as an equal of the USA leader.
The president who once described Kim as "Little Rocket Man" and threatened to destroy his country if it did not give up nukes, has not said what might happen if the summit goes the wrong way.
"It's unknown territory, in the truest sense", Trump said during the G-7. "And he has that opportunity, and he won't have that opportunity again", Trump said.
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