Mr. Kim’s recent announcement that North Korea no longer needs to test nuclear weapons or long-range missiles has left Japan acutely concerned that the North intends to keep what nuclear weapons it already has, and to maintain its arsenal of short- and medium-range missiles that can reach Japan.

An editorial in the right-leaning newspaper Yomiuri Shimbun called Mr. Kim’s announcement “a tactic to weaken the pressure of the international community’s sanctions,” adding that “there was no mention of any intention to abandon nuclear and ballistic missiles” in the statement.

Japanese officials “are trying to keep the conversation very focused on what ‘denuclearization’ means,” Ms. Smith said. “The experts that have been here before have had these conversations multiple times. They understand that when Kim Jong-un is talking about denuclearization he doesn’t necessarily mean the same thing that we mean, so there’s a lot of pressure to just put the brakes on, be cautious, make sure you know what you’re doing.”

Commentators in Japan speculated that Mr. Trump might also see some value in keeping Japan nervous.

“For President Trump, it may be favorable to keep Japan feeling left behind and facing a threat,” Park Il, an economics professor and expert on the Korean Peninsula at Osaka City University, said on a Tokyo Broadcasting System news program. “Japan will possibly have to buy more weapons for whatever price the United States sets.”

Besides the security concerns, the return of the Japanese citizens who were abducted by North Korea in the 1970s and ’80s is a top priority of Japan and Mr. Abe in particular.

Mr. Abe scored what appeared to be a diplomatic victory in Mar-a-Lago when Mr. Trump promised he would raise the issue directly with Mr. Kim.

“We’re going to do everything possible to have them brought back, and bring them back to Japan,” Mr. Trump said in a joint news conference with Mr. Abe. “I gave you that promise.”