WASHINGTON (CBSNewYork) — President Donald Trump on Thursday canceled the upcoming June 12 summit in Singapore with North Korean leader Kim Jong Un.

Speaking from the White House Thursday for the first time since cancelling the summit, Trump said, “while many things can happen” he believes “this is a tremendous setback for North Korea and a setback for the world.”

“Hopefully, everything’s going work out well with North Korea and a lot of things can happen,” the president said. “It’s possible that the existing summit could take place or a summit at some later date.” 

North Korea’s Foreign Minister Kim Kye Gwan said the North was still willing to sit down for talks with the U.S. “at any time, at any format.” In a statement carried by state media, he said Trump’s decision was “very regrettable” and showed how deep-rooted the hostility is between the U.S. and North Korea, and showed “how urgently a summit should be realized to improve ties.”

Earlier Thursday, the White House released a letter from the president to Kim that said Trump was “very much looking forward” to the summit.

“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,” the letter read. “Please let this letter serve to represent that the Singapore summit, for the good of both parties, but to the detriment to the world, will not take place.”

The president was referring to recent comments from North Korean Vice-Minister of Foreign Affairs Choe Son Hui directed at Vice President Mike Pence, saying, “I cannot suppress my surprise at such ignorant and stupid remarks gushing out from the mouth of the US vice-president.”

The North Korean government also referred to Pence as a “political dummy.”

In an interview on Fox News Wednesday, Pence had reiterated a comment National Security Advisor John Bolton had made comparing North Korea to Libya.

“This will only end like the Libyan model ended if Kim Jong Un doesn’t make a deal,” Pence said.

Under the Libyan model, leader Muammar Gaddafi dismantled his nuclear program in exchange for relief of sanctions. At first the agreement was seen as a success for denuclearization, but eight years later Gaddafi was overthrown and killed by Western-backed rebels.

In his letter, Trump went on to say that Kim talks about the North’s nuclear capabilities “but ours are so massive and powerful that I pray to God they will never have to be used.”

Earlier Thursday, North Korea said it demolished its only nuclear testing site after a series of explosions overnight, which had been planned by Kim ahead of the scheduled summit.

In his letter, Trump said he felt “a wonderful dialogue was building up between you and me, and ultimately, it is only that dialogue that matters.”

“If you change your mind having to do with this most important summit, please do not hesitate to call me or write,” the president said. “The world, and North Korea in particular, has lost a great opportunity for lasting peace and great prosperity and wealth. This missed opportunity is a truly sad moment in history.”

Trump also thanked Kim for the recent release of three Americans who were being held prisoners in North Korea, saying it was “a beautiful gesture and was very much appreciated.”

The president cast doubt on the summit earlier this week while meeting with South Korean President Moon Jae-in at the White House, saying there was a “very substantial chance” that the meeting wouldn’t happen as scheduled.

Some Democrats say the president should have seen this coming.

“The art of diplomacy is a lot harder than the art of the deal,” Sen. Bob Menendez, D-N.J., said. “It’s pretty amazing that the administration might be shocked that North Korea is acting as North Korea might very well normally act.”

Last week, the North pulled out of planned peace talks with the South, objecting to long-scheduled joint military exercises between U.S. and South Korean forces.

The North has also threatened to abandon the summit over U.S. insistence on rapidly denuclearizing the Korean peninsula.