The Japanese government protested Tuesday a visit by a South Korean politician to South Korean-administered, Japanese-claimed islets in the Sea of Japan.
The visit by the opposition lawmaker earlier Tuesday comes a few days before Japanese Prime Minister Fumio Kishida's two-day visit to Seoul starting Sunday amid thawed ties between the two countries.
Japan's Foreign Ministry lodged the protest saying that the visit on Tuesday to Takeshima, also known as Dokdo in South Korea, was "thoroughly unacceptable and extremely regrettable."
The two neighboring countries' ties have long been strained over wartime and territorial issues. Japan colonized the Korean Peninsula between 1910 and 1945.