Leaders of Japan, the United States and South Korea are planning to meet on the fringes of the Group of Seven summit next month, with trilateral cooperation in dealing with North Korea's nuclear and missile threats expected to be on the agenda, sources close to the countries said Saturday.

It would be the first time since 2017 for the countries to hold a trilateral summit. The sources said a separate meeting between Japanese Prime Minister Yoshihide Suga and South Korean President Moon Jae In is also being explored to coincide with the G-7 summit.

Combined photo shows (from L) Japanese Prime Minister Yoshihide Suga, U.S. President Joe Biden and South Korean President Moon Jae In. (Kyodo)

A trilateral summit would be a first under the administration of U.S. President Joe Biden who took office in January. The United States sees strong ties with Japan and South Korea as key in efforts to denuclearize North Korea and counter China's growing assertiveness.

Although ties between Tokyo and Seoul remain chilly over history-related issues, a source familiar with the matter said South Korea expressed hope to hold a summit with Japan during a recent meeting in Tokyo between its intelligence chief and Suga.

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Earlier this month, the foreign ministers of Japan, the United States and South Korea met in London, during which they affirmed close coordination to denuclearize the North.

G-7 host Britain has invited Moon as a guest to the in-person summit, which also brings together members Japan, the United States, Canada, France, Germany and Italy, plus the European Union.

The summit is slated for June 11 to 13 in Cornwall, southwestern England.