In a statement, the foreign ministry said it strongly objected to the Takeshima Day event held by Japan’s Shimane prefecture and to the attendance of a senior Japanese government official, urging Japan to immediately abolish the ceremony, Reuters reported.

The tiny ‌islets, known as ‌Takeshima in Japan and Dokdo ‌in South ⁠Korea, which controls ⁠them, have long been a source of tension between the two neighbors, whose relations remain strained by disputes rooted in Japan’s colonial rule of the Korean peninsula from 1910 to 1945.

“Dokdo is clearly South Korea’s sovereign territory historically, geographically and ⁠under international law,” the ministry said, calling ‌on Japan to ‌drop what it described as groundless ​claims and to face ‌history with humility.

The ministry summoned a top ‌Japanese diplomat to the ministry building in Seoul to lodge a protest.

A person at Japan’s foreign ministry said no one was available on Sunday to comment. ‌A call to the Prime Minister’s Office went unanswered. The government sent a ⁠vice-minister ⁠from the Cabinet Office, not a cabinet minister, to the ceremony.

Seoul has repeatedly objected to Japan’s territorial claims over the islands, including a protest issued on Friday over comments by Japan’s foreign minister during a parliamentary address asserting Tokyo’s sovereignty over the islets.

The territory lies in fertile fishing grounds and may sit above enormous deposits of natural gas hydrate that could be worth billions of dollars, Seoul has said.