The meeting, long sought by Pyongyang, will be the first ever between a serving U.S. president and a North Korean leader, and will focus on the nuclear bombs and ballistic missiles the North has spent decades developing.
"The Pentagon didn't know this was coming", Dr Green said.
That doesn't seem to pin the North down to the concrete and unilateral measures Trump said he would demand going into the talks and it remains to be seen what significant changes could occur now that they seem to be moving toward more peaceful relations. "It was a bad thing, it was brutal, but a lot of people started to focus on what was going on, including North Korea".
Turnbull echoed that line: "I want to say that I do not believe that summit would have occurred had it not been for the absolute solidarity on the very tough economic sanctions on North Korea that have been imposed by the UN security council, that's had the support, obviously, of the United States and Japan and Australia and other countries, but also China".
Ms Bishop has cautiously welcomed the overall progress in the summit but warned North Korea's denuclearisation must be thoroughly verified and dismissed Mr Trump's concession on military exercises.
Trump's pledge to end joint exercises with South Korea without explicit concessions from North Korea to lower the military threat posed by Pyongyang took South Korean and USA military officials by surprise.
A spokesman with Moon's office, who asked not to be identified to discuss internal deliberations, said the government was still trying to understand Trump's "exact meaning or intentions" with the military freeze.
At a news conference Tuesday following the summit, Trump said that as long as talks with the North were continuing, the USA would not carry out the joint exercises - which he called "war games", labeling them "provocative" and saying that the decision would save "a tremendous amount of money". In essence, Trump's money-focused transactional nature took only a few hours to surface after his handshake with Kim. The video offered Kim a stark choice between military conflict on the Korean Peninsula and the kind of robust economic development that has turned neighbouring South Korea into a wealthy nation.
How did South Korea react?
In talks with Kim on Tuesday in Singapore, Trump committed to an open-ended negotiating process and said the US would also suspend military exercises with South Korea.
"This is the weakest statement I have ever seen come out of any engagement with North Korea".
"Yeah, he's de-nuking, I mean he's de-nuking the whole place".
Yet Kimball is anxious by the hard history of negotiations with North Korea, combined with the lack of any timetable or road map for further steps in the latest agreement.
More broadly, Mr. Yun said he was "quite surprised" at the lack of a more specific commitment on denuclearization from the North Korean side.
The US stations around 30,000 troops in security ally South Korea to protect it from its neighbor, which invaded in 1950 in an attempt to reunify the peninsula by force.