Moon, who has lobbied hard for nuclear negotiations between Trump and Kim Jong Un, held a surprise meeting with the North Korean leader on Saturday in an effort to keep the summit alive.
He added: "One major difference is that the current process is a top-down process where Trump himself personally makes the decision "we will do the summit", "we will not do the summit"; and that kind of process may deliver extremely significant outcomes, but at the same time I think that there is a high risk that it would also lead to disastrous outcomes".
US Secretary of State Mike Pompeo and North Korea's former military intelligence chief held "substantive talks" in NY today.
On Wednesday, Kim Yong Chol, the vice chairman of the ruling North Korean Workers' Party's Central Committee, arrived in NY to hold talks with Pompeo as part of preparations for the US-North Korean summit in Singapore. "The meetings have been very positive".
Trump had been scheduled to meet Kim in Singapore on June 12, but the meeting was thrown into doubt after the USA leader said he was cancelling it. "The people of #NorthKorea can have a brighter future and the world can be more peaceful".
Commenting the meeting on Twitter, Mr Pompeo said: "Good working dinner with Kim Yong Chol in NY tonight".
"Most North Koreans have reacted positively to the recent North-South summit, plans for a North-U.S. summit, and the removal of the Punggye-ri nuclear test site removal because they can expect possible economic reform", he said, referring to a hope that harsh worldwide sanctions placed on the regime in response to its nuclear tests and ballistic missile launches may now be eased.
Activist Kim Young-hwan speaks at a symposium on North Korean human rights in Seoul on May 31, 2018. Shortly afterward, however, the U.S. president said that he was still open to the meeting with the North Korean leader. Spokeswoman Sarah Huckabee Sanders said Trump will host Japanese Prime Minister Shinzo Abe of Japan on June 7 to coordinate their thinking ahead of the summit.