President Joe Biden (left) poses for a photo with Fumio Kishida and Yoon Suk Yeol (right) in Hiroshima on Sunday. AP

The leaders met briefly on the sidelines of the G7 summit, to which host Japan invited South Korea as long-frosty ties between the neighbours thaw.

US President Joe Biden on Sunday invited the leaders of Japan and South Korea to formal three-way talks in Washington, a senior US administration official said.

The leaders met briefly on the sidelines of the G7 summit, to which host Japan invited South Korea as long-frosty ties between the neighbours thaw.

Tokyo and Seoul, both key US allies, have long been at odds over issues related to Japan's brutal 1910-1945 colonial rule of Korea, including sexual slavery and forced labour.

But South Korean President Yoon Suk Yeol and Japanese Prime Minister Fumio Kishida have made active efforts to restore soured ties since Seoul announced a plan to compensate those affected by wartime forced labour without Tokyo's involvement.

The official said the timing for the meeting would be worked out "soon," and there were no further details immediately available.

Earlier, Yoon and Kishida made a historic visit Sunday to a memorial for Koreans killed in the atomic bombing of Hiroshima.

It was the first time leaders of the two countries have jointly visited the memorial, and only the second time a Japanese prime minister has done so.

"This will be remembered as a courageous action by Prime Minister Kishida that paves the way for a peaceful future while expressing grief for the Korean victims of the atomic bombing," Yoon said at a bilateral meeting after the visit.