It also came a day after President Moon Jae-in of South Korea urged North Korea and the United States to resume dialogue to try to narrow their differences on how to denuclearize the North so that the South Korean leader could push his ambitious plan to integrate the economies of the two Koreas.

North Korea blamed a joint military exercise between South Korea and the United States when it started conducting its latest series of weapons tests last month. It mainly blamed South Korea for the exercise, saying that it could resume a dialogue with Washington, but not with Seoul, once the joint military exercise ends later this month. And Mr. Trump has complained more about the expense of the joint military drills than about the North’s missile tests.

President Trump has shrugged off North Korea’s recent weapons tests, calling them “smaller ones” that involved neither nuclear explosions nor intercontinental ballistic missiles. On Saturday, he said North Korea’s leader, Kim Jong-un, had sent him a letter with a “small apology” explaining that North Korea was conducting tests to counter the American military exercise with South Korea that Mr. Trump has himself criticized as too expensive.

Analysts said Mr. Trump’s downplaying of North Korea’s recent missile tests gave the country a green light to develop and test new short-range weapon systems that threatened not only American allies in South Korea and Japan but also American troops and civilians living there. Under a series of United Nations Security Council resolutions, North Korea is also banned from testing ballistic missile technology.

“Rather than denouncing these tests as violations of U.N. resolutions and as a threat to the American allies, President Trump has sounded as if he didn’t care, describing them as not a threat to the mainland United States,” said Kim Sung-han, a former vice foreign minister of South Korea who teaches at Korea University in Seoul. “His comments make the allies and American troops in the region more vulnerable to North Korean missile threats.”