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.
The US military has since announced that 100 wooden coffins have been moved to the inter-Korean border in preparation.
The expected North Korean officials never arrived, according to the official who requested anonymity as he was not permitted to talk publicly about the event.
The agreement on the return of remains of Americans believed to have been lost on the North Korean side of the border during the 1950-53 war, "including the immediate repatriation of those already identified", was the only concrete commitment on the four-point summit declaration.
During Mr Pompeo's trip relations between the USA and North Korea appeared to take a dive as Pyongyang accused the U.S. of a "gangster-like mindset" during the high-level negotiations.
An estimated 30,000 U.S. soldiers died in the 1950-53 Korean war.
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But Croatia found energy after the break when the game opened up, making England's missed first-half opportunities seem all-the-more significant.
North Korea's failure to show up to the meeting follows a tempestuous week in the ongoing denuclearization talks with Washington.
According to President Trump, returning the remains of USA troops was agreed upon during the Singapore summit. Identities would not be confirmed until after what is often a lengthy and complicated forensics process.
The letter comes days after the North Korean Foreign Ministry released a statement accusing the US of "ganster-like" demands and trying to unilaterally pressure the country into abandoning its nuclear weapons. Pompeo made his first overnight visit to Pyongyang last week to discuss a specific definition for denuclearization of the Korean Peninsula, which for America would require the complete elimination of the North Korean nuclear program.
Much progress has been made compared to 20 years ago but "significant humanitarian challenges" remain, Lowcock said.
Meanwhile, the United Nations is trying to raise $US111 million ($150 million) to meet health, water and sanitation and food security needs for about 6 million people in North Korea.
Trump called Kim "Little Rocket Man" or "Rocket Man" in several tweets in 2017 and early 2018 and has said that North Korea's continued threats against the US would be "met with fire and fury like the world has never seen".