President Trump has cancelled the upcoming summit between the United States and the North Koreans in a new letter released on Thursday. Mr. Trump writes in the letter that he was "very much looking forward to being there with you. 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."

He also told Kim in the letter, "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."

Read the letter here:

During remarks at the White House, Mr. Trump called the summit's cancellation a "tremendous setback" for the North Koreans and the world alike. He held open the possibility that the cancelled summit might still take place at a later date.

He also suggested that the U.S. stands "ready if necessary" for any possible responses to the summit being called off, adding that he had spoken to officials in South Korea and Japan, where they communicated that they are ready should "foolish or reckless acts" be taken by North Korea in response to the summit's cancellation.

He said that the countries are also "willing to shoulder much of the cost of any financial burden and the costs associated by the U.S. in operations if such an unfortunate situation is forced upon us."

"We are more ready than we have ever been before," Mr. Trump said. When asked if calling off the meeting raised the risk of war, the president replied "Well, we'll see what happens."

Follow live updates as this story develops:

North Korea responds to Trump canceling summit

The North Korean government is responding to President Trump's decision to cancel the planned summit.

South Korea's Yonhap News says Vice Foreign Minister Kim Kye-gwan issued a statement to the North's state-run Korean Central News Agency, saying North Korea was still willing to meet.

"We express our willingness to sit down face-to-face with the U.S. and resolve issues anytime and in any format," he said, according to Yonhap. "Our commitment to doing our best for the sake of peace and stability for the world and the Korean Peninsula remains unchanged, and we are open-minded in giving time and opportunity to the U.S."

He said the situation shows "how grave the status of historically deep-rooted hostile North Korea-U.S. relations is and how urgently a summit should be realized to improve ties."

President Trump on Friday welcomed the statement from North Korea saying it was still willing to meet despite cancelling the summit. Mr. Trump called the North's reaction "warm and productive" and expressed hope for "long and enduring prosperity and peace."

Ben Tracy says there could be lasting impact in North Korea

CBS News correspondent Ben Tracy, who is in North Korea, said there could be "lasting impacts"

"They will likely react with some form of anger, disappointment," Tracey said. "You could expect them likely to blame the U.S. for a breakdown in diplomacy here on the Korean peninsula. And if they wanted to, this could become an excuse to backtrack on some of the promises they've recently made with South Korea. So there could be some lasting impacts here, depending on how North Korea wants to play this."

Tracy also described his observation of a North Korean nuclear testing site, where North Koreans said they blew up some of their explosives. North Korea invited a handful of journalists to watch.

"What they did is in front of us, they strung explosives up inside these tunnels, they had three tunnels that were still remaining at the site, and they blew them up," Tracy said. These were major explosions."

"Now the problem is, this was a group of journalists. Nobody there is a nuclear expert. So we have no way of knowing if what they did in front of us actually does render that site completely unusable..." Tracy added.

White House official blames "trail of broken promises"

In a call with reporters, a White House official said the decision to call off the summit came down to a "trail of broken promises."

The president's letter to North Korea, which he dictated, blamed "tremendous anger and open hostility" in a recent North Korea statement. But the White House official cited North Korea's objection to a routine annual military exercise, North Korean's failure to show up when the U.S. sent an advance team to Singapore, an inability to verify North Korea's claims it destroyed its nuclear site, and unreturned communications as contributing reasons.

Trump's decision to call off summit

It was President Trump who made the decision this morning to call off the June 12 summit, CBS News' Margaret Brennan reports, according to a senior administration official. Mr. Trump met with Bolton, Pompeo, and the vice president. Some on the "staff level" -- specifically Kelly -- were also involved in the discussion. The decision to scuttle the summit came after a late-night huddle between Pompeo, Bolton, the vice president and the president, following the North Korean statement slamming Pence. The statement was issued after about 9 p.m. ET yesterday and then generated the late night conversation.

The regime's statement last night may have been the final straw, but in recent days, prospects for the summit itself had been dimming, as North Korea appeared to be trying to "move the goal posts" for the meeting, specifically on the issue of the military exercises. Mr. Trump alluded to this recently, when he had raised questions about whether the summit would take place.

Another factor was the North Koreans' silence over the past 5-10 days, Brennan reports. Communications had "basically ceased" in the words of this official despite outreach by Pompeo and South Korea. Moon Jae-in did not have much new information when he came to the White House two days ago.

Brennan was also told that Pence's recent reference to the so-called "Libya model" during an appearance this week on Fox News wasn't a deliberate effort to provoke the North. Pence had apparently been trying to clarify and use similar language to that of the president, when he talked about the "Libya model." The "Libya model," as far as North Korea is concerned, was an abject failure, given that Muammar Gaddafi ended up dead eight years after giving up his nuclear weapons program. Bolton suggested to Brennan on "Face the Nation" that the "Libya model" could be applied to North Korea, but after the North reacted poorly, Mr. Trump construed it as a threat that would apply only if Kim Jong Un did not denuclearize the Korean peninsula.

Secretary of State Mike Pompeo publicly claimed today during public testimony that Bolton's original remarks about Libya were not meant as a veiled reference to the death of Gaddafi in 2011, but rather to the process used by the Bush administration in 2003-2004 to disarm Libya and welcome it into the international community.

The change in tone from the North, referencing a nuclear showdown, and the military exercise rhetoric indicated that something was changing. The president has an "inkling" of what that is and has publicly suggested it that China may be meddling with the diplomatic efforts. Brennan specifically asked the official if the past few days of trade tension with China, as well as the decision yesterday by the U.S. to disinvite China from military exercises had accounted for the shift. This official said that is "definitely a piece of it."

That said, the President is still open to a meeting with Kim at a future date. The White House wants to see how the North responds to today's letter.

Asked whether Pompeo and Bolton seem to be saying different things when it comes to plans for the North, the official told Brennan that Pompeo simply has to take a different tone because he is the diplomat -- but that the two are on the same page.

South Korea's calls cancellation "embarrassing" in tweet

In a translated tweet from South Korea's Blue House, their presidential office, President Moon Jae-in expressed that it was "embarrassed and regretful that the North American summit was not held on June 12 that was scheduled. Denuclearization of the Korean peninsular and enduring peace are historic tasks that can not be abandoned or delayed."

The translated tweeted added, that the "sincerity of the parties who have tried to solve the problem has not changed."

According to Yonhap News Agency, Moon had urged leaders in the U.S. and North Korea to directly talk to each other Friday, hours before Mr. Trump's letter went public.

Singapore ministry "regrets" cancellation

Singapore's Ministry of Foreign Affairs tweeted that they "regret" that the scheduled summit "will no longer take place on 12 June 2018. Singapore hopes that the dialogue and efforts to find lasting peace and stability on the Korean Peninsula will continue."

Trump calls dialogue with Kim "wonderful"

Mr. Trump continued to commend Kim Jong Un for engaging in a "wonderful dialogue" with the U.S. despite the president calling off the June talks. He said that North Korea still wants to do what's right.

He suggested the leaders have had a good working relationship, noting the successful return of American hostages. "We didn't have to pay, we wouldn't have paid," he added.

The president also suggested that dialogue with the North Koreans was "very good until recently." He said he thinks he understands what went wrong, but declined to explain it. "Someday, I'll give it to you, you can write about it in a book," he told the press.

Trump calls summit cancellation a "tremendous setback"

Speaking from the White House, President Trump called the summit's cancellation a "tremendous setback" for the North Koreans and the world alike. He held open the possibility that the cancelled summit might still take place at a later date.

"Nobody should be anxious, we have to get it right," Mr. Trump said.

His message to Kim: "I am waiting", adding that current economic sanctions and the administration's maximum pressure campaign will continue. "I hope that Kim Jong Un will ultimately do what is right, not only for himself, but perhaps most importantly what's right for his people, who are suffering greatly and needlessly," the president said.

Mr. Trump noted that he had spoken to his military chiefs, including Department of Defense Secretary James Mattis, and suggested that the U.S. stands "ready if necessary."

The president said that he had also spoken to officials in South Korea and Japan, where they communicated that they are ready should "foolish or reckless acts" be taken by North Korea in response to the summit's cancellation. He said that the countries are also "willing to shoulder much of the cost of any financial burden and the costs associated by the U.S. in operations if such an unfortunate situation is forced upon us."

"We are more ready than we have ever been before," Mr. Trump said. When asked if calling off the meeting raised the risk of war, the president replied "Well, we'll see what happens."

Congressional reaction today on Trump cancelling summit

Reaction from Capitol Hill to the North Korea summit cancellation was swift. House Speaker Paul Ryan said in a statement that the U.S. must "continue to work with our allies toward a peaceful resolution, but that will require a much greater degree of seriousness from the Kim regime."

House Foreign Relations Chairman Ed Royce, said that the Trump administration should "continue to look for opportunities while applying maximum diplomatic and financial pressure against Kim Jong Un."

Sen. Tom Cotton, R-Arkansas, commended the president for "seeing through Kim Jong Un's fraud." He added, "As I have long said, our maximum-pressure campaign on North Korea must continue."

Sen. Bill Nelson, D-Florida, meanwhile placed blame on the administration, writing "The cancellation of this summit reveals the lack of preparation on the part of President Trump in dealing with a totalitarian dictator like Kim Jong Un. We've seen similar lack of preparation by the president in dealing with the leaders of China and Russia."

Senate minority leader Chuck Schumer responded on the senate floor, saying "The fear many of us had was that the summit between President Trump and Kim Jong-Un would be a great show that produced nothing enduring."

He added, "If a summit is to be reconstituted, the United States must show strength and achieve a concrete, verifiable, enduring elimination of Kim Jong-Un's nuclear capabilities."

Pompeo on summit cancellation

During questioning before the Senate Foreign Relations Committee, Pompeo told lawmakers that he was part of the discussions last night and this morning that led to the decision by Mr. Trump to cancel the summit.

Pompeo would not tell the committee whether the administration had informed South Korea that the summit would be cancelled before the letter was released, but he said that the U.S. and South Korea are in "lockstep."

He said he hopes that the parties will be able to return to where they were "six, eight, twelve weeks ago," and he expressed confidence that this would be laid out in "some detail" in the coming days.

WH official on summit cancellation

There were reports that the North's reaction to Pence's comments prompted the cancellation of the summit, but a White House official told CBS News' Jacqueline Alemany that there was too much focus on that, and the more salient development was that the North Koreans had threatened nuclear war against the American people in their statement Wednesday night.

Pompeo testifies before Senate after North Korea meeting news

Meanwhile, Secretary of State Mike Pompeo is answering questions from the Senate Foreign Relations Committee on the administration's foreign policy goals after testifying before the House Foreign Relations Committee one day before for over 3 hours. He started the hearing by reading the president's letter to Kim Jong-Un. Later he told lawmakers that America was "ready" for the summit with North Korea.

"We're rockin, we're ready. President Trump was prepared for this meeting. We were fully engaged to prepare for this meeting," Pompeo said.

He added when asked about the reasoning behind the cancellation, "I regret the statements that North Koreans have made over the past few days and the fact that we have not been able to conduct the preparation between our two teams that would be necessary to have a chance for a successful summit."

Pompeo added that between the direct talks he had with Kim, he believed the offer he brought to Kim was serious and that Kim believed it was a sincere effort.

"Over the past many days, we have endeavored to do what Kim and I agreed, to put teams together to prepare to work for summit and we received no response from them," he added.

North Korea nuclear test site destroyed Thursday

Just Thursday, North Korea announced it had destroyed its Punggye-ri nuclear test site. The planned dismantling was previously announced by North Korean leader Kim Jong Un ahead of the now-cancelled summit meeting with President Trump.

North Korean officials brought about two dozen international journalists to the testing area, in the northeast part of the country. CBS News correspondent Ben Tracy was the only U.S. broadcast network correspondent on hand to witness several large explosions at Punggye-ri. He was among about two dozen international journalists who had been brought to the site to witness what the North said was the decommissioning of the nuclear test site.

Trump keeps door open for new meeting

Mr. Trump also wrote to Kim Jong-Un he felt a "wonderful dialogue was building you and me," and continued, "Some day, I look very much forward to meeting you." He thanked Kim for the recent release of three American hostages, calling it a "beautiful gesture and was very much appreciated."

"If you change your mind having to do with this most important summit," he adds, "please do not hesitate to call me or write."

North Korea's comments to Pence

The letter's mention of "tremendous anger and open hostility" appear to refer to insults from the North Koreans directed at Vice President Pence.

North Korean Vice-Minister of Foreign Affairs Choe Son Hui, quoted by the state-run news agency, said of Pence Thursday, "I cannot suppress my surprise at such ignorant and stupid remarks gushing out from the mouth of the US vice-president."

Pence in a separate interview with Fox News on Wednesday, seemed to threaten the North. "You know, as the president made clear, this will only end like the Libyan model ended if Kim Jong-un doesn't make a deal."