"I'm very honored to have helped the three folks", he said.
"The next few weeks will be critical, requiring air-tight coordination between our two countries", Kang said.
Welcoming the detainees back to the United States, he called it "a special night for these three people".
"We have a meeting scheduled in a very short period of time". Last year, North Korea tested intercontinental ballistic missiles such as the Hwasong-14 and Hwasong-15.
Pompeo was the head of the Central Intelligence Agency for 15 months prior to being sworn in as Secretary of State on April 26. In a joint news conference with South Korea's top diplomat, he offered a glimpse of what US-North Korean relations could look like if they succeed in reaching a nuclear accord.
Korea watchers have cautioned that North Korea may have something different in mind than the US when it says it's willing to go down a path of denuclearization.
In a tweet last week, Trump hinted at their impending release, saying that "the past Administration has always been asking for three hostages to be released from a North Korean Labor camp, but to no avail".
Following the Moon-Kim summit, Moon's office said Kim was willing to disclose the process to global experts, but the North's statement on Saturday did not include any mention about allowing experts on the site.
"Now that North Korea has accepted in principle that agreements should be verified, USA negotiators should hold them to this standard for any subsequent agreement", said Adam Mount, a senior defense analyst at the Federation of American Scientists. He was accused of unspecified 'hostile acts. Add North Korea as an interest to stay up to date on the latest North Korea news, video, and analysis from ABC News.More news: Robert Wickens Continues Veteran Showing in IndyCar Grand Prix
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Exchanging prisoners for an opening with the West has been a common tactic of Pyongyang over the years. However, he was released in June 2017, gravely ill and in a coma. "The United States no longer makes empty threats".
But a Japanese government source said it is "uncertain how seriously Trump will act on behalf of Japan" because of his "America First" policy.
"I must tell you that I want to pay respects to Otto Warmbier, who was a great man who really suffered", he said.
Kang said South Korea wanted the sanctions to stay in place until Pyongyang takes "visible, meaningful action" to get rid of its nuclear weapons.
"President Trump thanked Prime Minister Lee for his willingness to host President Trump's June 12 meeting with North Korean leader Kim Jong Un", the White House said in a statement. The previous three American presidents, Republicans and Democrats alike, have all negotiated flawed nuclear deals with North Korea.
Trump, surrounded by journalists and cameras earlier on Thursday also teased the "highly anticipated meeting".
The American said he had "good" and "substantive" conversations with Mr Kim during his visit.
In June 2008, worldwide broadcasters were allowed to air the demolishing of a cooling tower at the Nyongbyon reactor site, a year after the North reached an agreement with the U.S. and four other nations to disable its nuclear facilities in return for an aid package.