Kim Jong Un in June.
But many risks remain in doing business with North Korea, including its secrecy and chronic power shortages, said Lee Chul, former president of South Korea's state-run railroad operator.
Immediately after the summit Mr Trump announced there was "no longer a nuclear threat from North Korea". "We will work very closely, as I said, with the secretary of state and what he needs done we will certainly do to reinforce his effort".
Earlier Wednesday, Defense Secretary Jim Mattis issued a statement that three military exercises were suspended "in order to provide space for our diplomats to negotiate the verifiable, irreversible and complete denuclearization of the Korean peninsula".
Japan and North Korea had a "secret" meeting in Vietnam in July without informing the United States, the Washington Post reported Tuesday.
A recently published report suggests North Korea is set to hold a blockchain-related conference in the beginning of October, in a move that experts believe is being made to "show off" technological capabilities.
Retired Army Col. Doug MacGregor, who also spoke alongside Terry, said the US should declare an end to the Korean War and do whatever it needs to reassure North Korea that the USA does not plan to invade them.
"They basically don't think we're doing enough", a senior USA official told Reuters.
North Korea has warned that denuclearization talks are "again at stake and may fall apart", leading to the resumption of "nuclear and missile activities".
North Korea consistently complains that large-scale annual joint exercises, which usually take place in the spring and summer, are preparations to invade.
Last week, Trump cancelled a meeting between Secretary of State Mike Pompeo and North Korean officials, citing insufficient progress on denuclearisation.
A December 2015 North Korean investment brochure, seen by Reuters, says Pyongyang aims to build an "international rapid transit railway" to promote its special economic zone in the western city of Sinuiju bordering China.