For about 70 years since the Korean War, the US and North Korea have been hostile to one another.
"North Korea is well beyond what these other countries had", Heinonen said.
North Korea's climb down on nuclear weapons comes after Trump determinedly maintained a raft of economic sanctions against the country.
The girls mentioned meeting Kim Jong Un, and said, "We knew he was coming to the concert but we didn't know we would actually get to meet him".
Kim said he would invite security experts and journalists to the North to observe the closure of the site, the Souths presidential Blue House said.
Google Earth image of Mt. Mantap in North Korea showing the locations of the nation's six nuclear bomb tests, including the September 3, 2017, test (red), the largest, which lowered the mountain by 20 inches.
South Korean newswire, Yonhap, quoted a statement from the North's ministry of foreign affairs as confirming that the country would take "technical measures" to dismantle its Pyunggye-ri nuclear test facility.
The summit will be the first meeting ever between a sitting U.S. president and the leader of North Korea.
However, both Kang and Pompeo said that they agreed on the need for the "total, permanent and verifiable" denuclearization of the divided peninsula.
He is now preparing for the first ever face-to-face meeting between a sitting American president and a North Korean leader, scheduled for June 12 in Singapore.
North Korea's human rights issues weren't specifically mentioned in a joint statement announced by Mr. Moon and Mr. Kim after their summit last month.
North Korea for decades has been pushing a concept of "denuclearization" that bears no resemblance to the American definition.
A United Nations human rights expert has welcomed the release of three U.S. nationals by North Korea, saying the move was "another important building block for the prospects of peace" for the two Koreas and beyond.
But in September 2008, the North declared that it would resume reprocessing plutonium, complaining that Washington wasn't fulfilling its promise to remove the country from the USA list of state sponsors of terrorism.
The talks, which are expected to last a day, are set to focus on North Korea's rapidly advancing nuclear and ballistic weapons programs.
Choi believes his father was executed in North Korea in 1970.
That was also when South Korea began deploying anti-ship missiles and strengthening its fleet of patrol ships in its western seas, which made North Korean hijacking operations more hard, analysts say.
According to South China Morning Post, a group of Chinese geologists concluded the powerful sixth nuclear test had turned the mountain "into fragile fragments", which could allow radioactive dust to escape through cracks or holes.