The remark was made following a report by Japanese broadcaster NHK stating that Japanese Foreign Minister Taro Kono is planning to visit Seoul to meet his South Korean and US counterparts one day after the Trump-Kim summit.

"We are in talks with the US over our diplomatic schedule after the summit," the official said, adding that nothing has been decided yet regarding the Japanese minister's visit to South Korea.

The White House announced Monday that the first US-North Korea summit will start at 9 a.m. next Tuesday in Singapore.

Trump earlier called off the meeting, citing the North's "tremendous anger and open hostility" toward the United States, but agreed to look into the possibility of going ahead with the proposed summit after a ranking North Korean official visited him last week with a letter from the North Korean leader. (Yonhap)