The top Democrat on the Senate Intelligence Committee has asked the head of USA intelligence to assess whether North Korea's posture and actions regarding denuclearization match up with the Trump administration's claims.
According to estimates from the Pentagon, 7,700 US troops are still unaccounted for from the Korean War.
But U.S. Defense Department and United Nations Command officials were left waiting in the DMZ's Joint Security Area, with no immediate explanation for the North Korean absence, according to South Korean's Yonhap news agency and U.S. officials who spoke to CNN and The Washington Post.
At the Singapore summit on 12 June, Mr Trump and Mr Kim signed a document that included a pledge from North Korea to rid the Korean peninsula of nuclear weapons. But the North Korean leader never showed up during Pompeo's three-day visit.
Stormy Daniels Poses for Glamorous Mugshot Following Arrest at Ohio Strip Club
Daniels, whose real name is Stephanie Clifford, is in the middle of a scandal that some say could topple the USA president. Representatives for the Columbus Division of Police did not immediately respond to ABC News' request for comment.
Since the summit in Singapore, there has been increasing scrutiny of the agreement reached by Trump and Kim, with some experts suggesting that North Korea did not really intend to give up its nuclear weapons.
Kim's letter also predates a planned meeting over the return of U.S. remains on Thursday on the North Korean-South Korean border, where American military officials were stood up by their North Korean counterparts. The U.S. also risks giving the North Koreans leverage to continue diplomacy and drag out disarmament talks.
The letter comes days after the North Korean Foreign Ministry released a statement accusing the USA of "ganster-like" demands and trying to unilaterally pressure the country into abandoning its nuclear weapons.
Several days previously, Pyongyang had slated the United States for seeking unilateral and forced denuclearization from North Korea.
Trump was in London to meet with United Kingdom leaders after leaving the North Atlantic Treaty Organisation summit in Brussels, Belgium, when he tweeted Kim's letter. Pyongyang has asked the UN Command Armistice Commission to upgrade the talks to a higher level to include a US general, South Korea's foreign ministry said. Pompeo has called the meetings "productive" while North Korean state media referred to Pompeo's posturing in meetings as "gangster-like".
North Korea could be looking for an opportunity to build on the momentum of the latest developments, including the cancellation of a joint U.S.