Trump called it a "truly sad moment in history."
"Sadly, based on the tremendous anger and open hostility displayed in your most recent statement, I feel it is inappropriate, at this time, to have this long-planned meeting. Therefore, please let this letter serve to represent that the Singapore summit, for the good of both parties, but to the detriment of the world, will not take place."
According to a senior White House official, President Trump “dictated every word” of the letter to Kim Jong Un himself.
The president made the decision to cancel the summit following a briefing Wednesday night after North Korea issued a scathing statement calling Vice President Mike Pence a "political dummy", the official said. North Korea was deeply critical of comments Pence made suggesting that the so-called Libya model could be applied to North Korea if Kim doesn't make a deal with President Trump amid threats to pull out of the summit.
At the U.S.'s urging, under the leadership of Col. Muammar el-Qaddafi, Libya, nixed its early-stage nuclear program. Years, later he was ousted and killed with help from NATO-backed troops.
"Whether the U.S. will meet us at a meeting room or encounter us at nuclear-to-nuclear showdown is entirely dependent upon the decision and behavior of the United States," the North Korean statement read.
President Trump met again early Thursday morning with his team, including Chief of Staff Mike Kelly, Vice President Mike Pence and spoke with Secretary Mike Pompeo and national security adviser John Bolton before making a decision to dictate the letter.
And, in an apparent response to the North Korean threat, the president issued a threat of his own in his letter — warning about the United States' "massive" nuclear capabilities.
"You talk about your nuclear capabilities, but ours are so massive and powerful that I pray to God they will never have to be used," Trump writes.
In the letter, the president leaves open the possibility of meeting at a future date, telling Kim to reach out to him directly by phone or letter if he decides he would like to meet.
"Someday, I look very much forward to meeting you," Trump writes. "If you change your mind having to do with this most important summit, please do not hesitate to call me or write."
The summit cancellation and tense missives were the latest ratcheting up of tensions as the anticipated meeting date loomed.
The U.S. was concerned over North Korea’s objection to U.S.-South Korea military drills. And American officials didn't appreciate being stood up at last week’s planning meeting in Singapore.
“They waited and they waited, the North Koreans never showed up," the senior White House official told reporters. "The North Koreans didn't tell us anything, they simply stood us up.”
The official also cited North Korea’s refusal to allow international experts/officials to Thursday’s nuclear test site demolition – violating a promise Pyongyang allegedly made to both the U.S. and South Korea.
The North Koreans simply went dark, the official said.
“The United States has over the past week made numerous attempts to communicate with the North Koreans but they have not responded," the officials said. "In fact, the first communication we received in a week arrived last night in the form of a propaganda release.”
The official's comments echoed Trump's own sentiments shared earlier in the day that "there's been a very good working relationship" with Kim and lamenting about how it recently seemed to spiral downward.
In the president's letter to Kim, Trump referenced the "wonderful dialogue [that] was building up between you and me".
The president would not elaborate further, though earlier in the week he suggested Chinese President Xi Jinping may have privately urged Kim in a recent meeting to take a tougher stance in negotiations with the U.S.
"I will say I'm a little disappointed, because when Kim Jong-un had the meeting with President Xi, in China," Trump said Tuesday. "I think there was a little change in attitude from Kim Jong-un."
Trump called the summit's cancelation a "tremendous setback for North Korea and, indeed, a setback for the world".
He also said that he has spoken with Defense Secretary James Mattis and the Joint Chiefs of Staff to ensure the U.S. military "is ready if necessary".
Asked by ABC News if the breakdown of the summit raises the risk for war with North Korea, Trump would not answer definitively.
"We'll see what happens," Trump said. "I really think they want to do what's right."