Washington (CNN) President Donald Trump will not meet North Korean leader Kim Jong Un next month, he announced in a letter to Kim released by the White House Thursday morning, scrapping plans for what would have been a historic diplomatic summit.

He said during an appearance from the Roosevelt Room the decision amounted to a "tremendous setback" and warned North Korea that the US military is ready to act should Pyongyang take any "foolish and reckless" action.

"Our military, which is by far the most powerful anywhere in the world that has been greatly enhanced recently as we all know, is ready as necessary," he said.

But he left open the door to renewing the diplomatic thaw which had preceded the anticipated talks.

"If and when Kim Jong Un chooses to engage in constructive dialogue and actions, I am waiting," he said.

In his letter, which the administration said was dispatched through established communication channels to North Korea, Trump wrote with chagrin the summit was off.

The full letter from the President Trump to Chairman Kim Jong Un : https://t.co/RJD9qV0HSl pic.twitter.com/b0BEf0mKWf — The White House (@WhiteHouse) May 24, 2018

"I 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," Trump wrote. "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."

Trump and Kim were scheduled to meet in Singapore on June 12, for what would have been the first face-to-face meeting between a US and North Korean leader.

Months of diplomatic advances

The decision ends months of diplomatic advances between the US and North Korea that Trump repeatedly heralded as the likely precursor to a historic peace deal and the denuclearization of North Korea. Now, the détente between Washington and Pyongyang appears in jeopardy, with a return to the bellicose rhetoric that has defined the US-North Korea relationship for much of Trump's presidency once again peering over the horizon.

In his letter, Trump signaled a return to the bitter nuclear back-and-forth that colored his early interactions with Kim before the diplomatic opening.

"You talk about your nuclear capabilities," Trump wrote in his letter to Kim, "but ours are so massive and powerful that I pray to God they will never have to be used."

Still, Trump signaled direct talks with Kim could still be in the offing, writing that he "felt a wonderful dialogue was building up between you and me" and that he looks forward to meeting Kim "some day."

Even as the summit was canceled, North Korea was taking at least precursory steps to scale back its nuclear program. The regime appeared to destroy at least three nuclear tunnels, observation buildings, a metal foundry and living quarters at its Punggye-ri nuclear test site on Thursday, in a process observed by invited international journalists including CNN's Will Ripley.

No weapons inspectors or nonproliferation experts were invited to witness the event, and it was unclear whether the explosions rendered the tunnels inoperable, or only caused limited damage.

How it happened

Trump withdrew from the summit after a North Korean vice minister of foreign affairs slammed Vice President Mike Pence on Wednesday as a "political dummy," the latest harshly worded statement from Pyongyang.

Trump and his aides were infuriated by the statement and wanted to respond forcefully, multiple people familiar with the situation told CNN. The specific and personal targeting of Pence is what irked US officials, three people familiar with the matter said.

The verbal broadside against Pence was just the latest harshly worded statement from North Korea over the last 10 days. Early last week, North Korea canceled a planned meeting with South Korea and threatened to pull out of the Singapore summit because of ongoing US-South Korean military exercises.

Trump and his aides had insisted over the past week that planning for the summit was still ongoing amid the increased bluster from Pyongyang. A logistics team was dispatched to Singapore to finalize details with North Korea officials. And a commemorative coin was stamped by military aides labeling Kim the "Supreme Leader."

Not entirely a surprise

Still, the collapse of the summit was not entirely a surprise, even if Thursday's announcement was abrupt. North Korea has offered diplomatic openings to the United States several times over the past decades, only to return to bellicose threats. Even after Trump accepted Kim's invitation to meet in March, most administration officials put the likelihood of the summit actually happening at less than 50% -- and administration officials grew increasingly skeptical over the last week.

US officials had also grown increasingly skeptical of Pyongyang's commitment to denuclearization. On Wednesday, CNN reported the Trump administration was looking to have additional high-level talks for assurances from Kim for complete denuclearization before the summit went ahead.

Hours later, a North Korean official lashed out at Pence and said Pyongyang is ready for a nuclear showdown if dialogue with the United States fails.

Choe Son Hui, a vice-minister in the North Korean Foreign Ministry, said if the US continued on its current path, she would suggest to North Korea's leadership that they reconsider the planned summit between Trump and Kim.

"Whether the US 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," Choe said in comments carried by North Korea's state-run KCNA news agency Thursday.

Choe was responding to comments by Pence made Monday during a Fox News interview that she deemed "unbridled and impudent."