This comes at a time when a report compiled by Korea Development Bank, a state-run financial institution in South Korea, has claimed that evidence had emerged of a small-scale cryptocurrency mining operation being run by the North Korean regime a year ago between May and July.
And the summit itself was called off in May - Mr Trump citing Pyongyang's "open hostility" - only for it to take place after all.
South Korea today expressed disappointment over the USA decision to call off Secretary of State Mike Pompeo's planned trip to North Korea, but insisted that continued diplomacy was vital to resolving tensions with Pyongyang.
U.S. intelligence and defence officials have repeatedly expressed doubts about North Korea's willingness to give up its nuclear weapons and did not expect Mr Pompeo's trip to yield positive results.
The United States is pressing North Korea to give up its nuclear weapons program, calling for stringent implementation of tough U.S. and U.N. sanctions.
In another tweet, Trump blamed the trade relationship with China, in part, for the lack of progress in denuclearizing the peninsula.
In South Korea earlier this month, President Moon Jae-in outlined plans for broad economic cooperation with the North, including joint economic zones on the border and a rail network.
The expert added that by making these remarks, Trump hopes to blame China, and not himself for lacking of progress in the U.S. -DPRK negotiations.
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But since then there have been several reports that it is failing to dismantle nuclear facilities.
Trump and Kim made history by holding the first-ever summit between their two countries, which have been locked in conflict since the 1950-53 Korean War ended in an armistice instead of a peace treaty.
With this as the backdrop and no real outline of its commitment to denuclearization, Donald Trump cancelled Mike Pompeo's visit to Pyongyang.
Moon turned aside concerns from the conservative political opposition that his government was moving too quickly in its overtures to the North.
Former U.S. ambassador to South Korea Christopher Hill praised the decision to cancel the upcoming trip, saying it looks like Trump "has begun to worry about #NorthKorea intentions".
After speaking with Trump by phone on Wednesday, Abe said Tokyo and Washington are in "complete agreement regarding the policy of realizing complete denuclearisation of the Korean peninsula", and said he raised the abductees as the issue "most important of all".
Pompeo and other administration officials have suggested some concessions short of easing or lifting sanctions are possible before verified denuclearization, but have refused to be specific about what they could be.
Simon Denyer, The Washington Post •.
Kawasaki, 76, who was born in Japan and lived for 43 years in North Korea before defecting, has not seen her children, still in North Korea, for years.