The prospect of a possible breakthrough summit between Washington and Pyongyang has left Tokyo jittery that U.S. President Donald Trump, under his banner of "America First," may settle for a major policy compromise that prioritizes U.S. homeland security while disregarding allied Japan's vulnerability to North Korean missiles, experts said Wednesday.

In his meeting with a high-level South Korea delegation Monday, North Korean leader Kim Jong Un was quoted by the South Korean government as saying he was open to talks with the U.S. to discuss denuclearization and the normalization of bilateral ties.

Despite the shifting ground, Prime Minister Shinzo Abe told Katsuyuki Kawai, his special diplomatic adviser currently in Washington, that Japan will continue to pressure the North for the time being, Kyodo News reported Wednesday. Kawai was quoted as telling reporters that Abe considers the latest overtures by the regime a sign that international sanctions and the increased monitoring of "ship-to-ship transfer" of goods involving North Korean vessels have been working.