North Korea has recently indicated that if the United States and South Korea did not cancel a joint military exercise planned for next month, it would scuttle efforts to resume negotiations with Washington and even resume nuclear and long-range missile tests. Analysts said that its recent short-range weapons tests were a warning that if its demand was not met, the North might escalate tensions with longer-range missile tests.

Weeks before Mr. Kim met with Mr. Trump in Singapore in June last year in the first-ever summit meeting between North Korea and the United States, Mr. Kim announced a moratorium on his country’s nuclear and intercontinental ballistic missile tests. Mr. Trump has since repeatedly touted the absence of such tests as his biggest diplomatic achievement in dealing with Mr. Kim.

With North Korea’s latest tests involving short-range missiles, Mr. Kim did not abandon his moratorium. But they violated the United Nations Security Council resolutions that bar the country from developing or testing ballistic missile technologies, South Korean officials said.

North Korea also recently unveiled a new submarine, indicating that it was pressing ahead with efforts to expand its submarine-launched missile capabilities. Such technology would extend the reach of its nuclear missiles and improve its capability to retaliate if its land-based launching sites were attacked.

Speaking to lawmakers on Wednesday, South Korean defense officials said that the new submarine appeared to be equipped with three missile launch tubes, an advance from an earlier model, which had only one.

Mr. Trump downplayed the significance of the North’s recent missile tests last Thursday, calling them “smaller ones” and repeating that he was still getting along “very well” with Mr. Kim.

“My relationship with Kim Jong-un is a very good one, as I’m sure you’ve seen,” Mr. Trump told reporters on Tuesday. “I like him; he likes me. We’ll see what happens.”