An agreement to return the remains of U.S. service members was touted by the Trump administration as one of the commitments secured during the president's historic summit with Kim on 12 June. USA intelligence analysts said in the wake of the summit that Pyongyang is working to hide key elements of its program, including the number of weapons it maintains and secret production facilities.
North Korea has said eight of the 17 - including Megumi Yokota, who disappeared while heading home from school when she was 13 - have already died, while four never entered the country, an account Japan has dismissed as unreliable.
Senate Intelligence Committee Chairman Mark Warner, D-Virginia, wrote to Director of National Intelligence Dan Coats on Thursday, asking him to answer a number of questions related to North Korea's progress, in light of statements made by President Trump and Secretary of State Mike Pompeo.More news: Serena Williams cruises into 10th Wimbledon final
Kim did not meet with Pompeo during his visit this month, viewed widely by foreign affairs analysts as an intentional slight since the two had met twice previously in Pyongyang.
Other speculation is that North Korea was discomforted with the way it was portrayed by the US media _ as trying to make money from the war remains.
There are about 7,700 U.S. soldiers classified as missing in action from the war.More news: Emmy Nominations: Modern Family, This Is Us and More Snubs and Surprises
On Monday, the president shared his confidence that the North Korean leader would live up to the agreement both leaders signed in Singapore. "Great progress being made", Trump said in a tweet that also included a copy of the correspondence from Kim.
Pompeo insisted the talks were making progress but as soon as he left, the North's foreign ministry berated him over his "unilateral and gangster-like" demands and for offering no constructive steps on the U.S. side.
There was no call or explanation from North Korean officials on why they skipped the meeting.
Pompeo last week failed to demonstrate any progress on denuclearization talks, leading one source with knowledge of the discussions to say the White House felt it went "as badly as it could have gone".More news: Amazon Prime Day sale: Best offers and how to get them