The White House has announced that the United States will not participate in a planned meeting with North Korea’s leader. The meeting with North Korean leader Kim Jong-un had been scheduled for June 12 in Singapore. President Donald Trump said, “I believe this is a tremendous setback for North Korea and, indeed for the world.”

In March, the world was stunned when President Trump spontaneously accepted Mr. Kim’s invitation to meet. The decision caught his entire national security team off guard. Some with knowledge of the matter say there was less than a 50 percent chance that the meeting would ever actually occur.

Notice of the cancellation of the summit was made in a letter from President Trump to Mr. Kim. In the letter, he cited a flurry of hostile statements and derisive comments about Vice President Mike Pence for the cancellation. A North Korean official had referred to Mr. Pence as a “political dummy”.

Mr. Trump wrote to Mr. Kim, “Based on the tremendous anger and open hostility displayed in your most recent statement, I believe it is inappropriate, at this time, to have this long-planned meeting.” The letter continued, “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.”

Mr. Trump’s letter left open the possibility that a meeting could get back on track. Mr. Trump said in a statement, “It’s possible that the existing summit could take place, or a summit at some later date. Nobody should be anxious. We have to get it right.”

North Korea reacted coolly to the news of the cancellation. Choe Son Hui, a vice foreign minister, said, “We will neither beg the U.S. for dialogue nor take the trouble to persuade them if they do not want to sit together with us.”

Both sides had made a series of conciliatory moves in the past few weeks aimed at keeping diplomatic channels open. North Korea pledged to halt nuclear and missile tests and released three Korean-Americans imprisoned there. Mr. Trump said that he would be open to a phased denuclearization of North Korea, provided its nuclear program was rapidly shut down.