He became the highest level figure from North Korea to hold talks at the White House since a senior envoy visited former US President Bill Clinton in 2000.
South Korea's unification and defence ministries declined to confirm the report, while an official at the Unification Ministry said the government was watching the leadership situation in the North very closely. North Korea's leadership is believed to regard nuclear weapons as crucial to its survival.
This could be a sign that the North Korean leader is "pursuing a new policy to become a developing country without nuclear weapons, rather than a poor country with nuclear weapons", he said.
There was initially much uncertainty over whether the summit would go ahead at all, and it was briefly called off last month by Mr Trump after a dispute with the North Koreans.
She said an "advance team" in Singapore was finalising logistical preparations and will remain in place until the summit begins.
Last month, North Korea interrupted the détente that had been developing on the peninsula by cancelling high level talks with South Korea and publishing vitriolic attacks against the USA in state media.
South Korea's Blue House on Monday quashed suggestions a formal end to the Korean War could be announced at the Trump-Kim summit.
The removal of top North Korean military officials from their positions is inviting speculation about internal instability in the Kim Jong Un regime.
All trade deals could be off, China warns US
Germany is also hoping its steel exports to the United States will be exempted from sanctions. The two countries have threatened tit-for-tat tariffs on goods worth up to $150bn each.
"We have sanctions on, they are very powerful and we would not take those sanctions off unless North Korea denuclearised".
The former USA ambassador to the United Nations has been described as one of the most ardent hawks against North Korea, and has received widespread criticism for his approach on dealing with the regime. The official handed him a letter from Kim Jong-un.
Secretary of State Mike Pompeo, who was present at the meeting where Kim handed Trump a symbolic letter, reportedly told Trump that Bolton's presence would be "counterproductive", people familiar with the talks told CNN.
Tokyo says Pyongyang kidnapped at least 17 Japanese in the 1970s and 1980s to teach Japanese language and culture to North Korean agents.
North Korean leader Kim Jong Un inspects the construction of the "Wonsan-Kalma shore Tourist Zone" in this undated photo released by KCNA in Pyongyang May 25, 2018.
But he also emphasized the economic aspects of Kim's move.
"No is a person who has come to the fore in the Kim Jong Un era, as a up-and-coming and trusted aide". I said, 'What's the objective of that?'" He continued, "If it's a positive meeting, I love it.