Kurt Campbell, who served as assistant secretary of state for East Asian and Pacific affairs in President Barack Obama's first term, said Pyongyang would be facing hard-line opposition to its provocations, the Tokyo Shimbun reported Wednesday.
Speaking at a symposium in Washington, D.C., Campbell also said the United States and Japan need to strengthen their alliance in preparation for all scenarios on the Korean peninsula, Japanese newspaper Mainichi Shimbun reported.
The alliance needs to upgrade because the bilateral relationship has changed completely, Campbell said.
It is no longer the case that the United States makes most of the decisions on security issues, and Japan stayed satisfied with the status quo, he said, according to the Japanese press report.
Campbell also called Tokyo's policy of strengthening the alliance while pursuing its own diplomacy a sound development.
In the meeting, Abe said he would actively seek negotiations with Moscow on the Kuril Islands dispute, according to Campbell.
In late September, a Japanese newspaper reported Tokyo was trying to resolve the long-running dispute with Russia over the four islands by negotiating the return of two of the islands, but Tokyo denied the report.
Clinton has stressed the importance of strengthening U.S. alliances with countries like Japan and South Korea, while Trump has suggested China take more responsibility for North Korea while falsely charging Korea and Japan of not paying for U.S. security.
In a recent interview with The New York Times, Johnson could not name the leader of North Korea, Kim Jong Un.
In early September Johnson had asked, "What is Aleppo?" when asked about his answer to the problems of the city at the focus of the Syrian civil war and humanitarian crisis.