"I think he's trying to pile on to the White House message after the suspension of the Pompeo trip that the United States is not satisfied with where North Korea is right now with denuclearization", he said after a panel discussion at the Center for the National Interest (CFTNI) on Tuesday.
But on Wednesday, Moon's office said he was intent on working as a mediator between Kim and Trump, just as he helped broker their first meeting in June.
Despite North Korea's recent calls for the South to take inter-Korean affairs into its own hands, the USA has repeatedly stressed that inter-Korean ties must advance in lockstep with progress on denuclearization.
But it's far from clear how infrastructure would be defined under the United Nations sanctions, and the French rail operators told Reuters they had no plans to team up with North Korea.
Mr Trump caught many American military planners off guard when he announced after an unprecedented summit with Mr Kim on June 12 that the United States was suspending this summer's joint military drills with South Korea, while North Kore would move to denuclearise.
China, North Korea's traditional ally and main trading partner, joined the USA in adopting tough global sanctions against Pyongyang in 2017, which the Chinese government says it is still enforcing.
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'China makes it much more hard in terms of our relationship with North Korea, ' Trump said at the White House on Wednesday, though he insisted his ties with Chinese President Xi Jinping were 'great'.
Last week Trump abruptly cancelled a visit to Pyongyang by US Secretary of State Mike Pompeo within 24 hours of announcing it. "With North Korea and the USA remaining stalemated, there is an even bigger need for an inter-Korea summit", Kim Eui-kyeom, a spokesman for the presidential Blue House, told a briefing. Since most wargames in South Korea simulate an invasion of North Korea, they do indeed tend to raise tensions significantly.
The statement also said that the USA trade dispute with China and other differences "will be resolved in time by President Trump and China's great President Xi Jinping".
The US president said he was not considering resuming joint military exercises on the Korean Peninsula that Pyongyang considers "provocative". It has also suspended nuclear tests and test-missile firings.
A test operation of a train connecting the South's capital of Seoul to the North's Shinuiju, which lies on the border with China, was initially planned for August 22-27 as part of the Koreas' joint field survey on modernizing cross-border railways, according to the Unification Ministry.
On Wednesday, State Department spokeswoman Heather Nauert told reporters that Washington believes "denuclearization has to take place before we get to other parts", confirming that included such a declaration. "We are doing this in conjunction of allies and partners", said Gen. Dunford. "Because if he came back empty handed again, then that really could be a dead end", said Abrahamian.
U.S. intelligence and defense officials have repeatedly expressed deep doubts that Pyongyang is serious about denuclearization.