Japan protests South Korean survey ship near Takeshima

Japan’s Coast Guard confirmed a South Korean survey ship, the Tamhae 3, was conducting an unauthorized marine survey inside Japan’s exclusive economic zone west of the Takeshima islets on August 7, prompting formal protests from Tokyo, Japan’s Foreign Ministry and Coast Guard said.

A Japan Coast Guard patrol vessel spotted the Tamhae 3 at around 1:33 p.m. on August 7, roughly 17 nautical miles (31 kilometers) west of Takeshima, extending what appeared to be a wire-like device into the water from its stern. South Korea had not submitted a prior request for Japan’s consent to conduct the survey, according to Japan’s Foreign Ministry.

The Coast Guard’s patrol boat radioed the Tamhae 3 to demand it halt the activity, saying marine research without Japan’s consent was not permitted. The survey ship crossed the geographic midline to the west at around 6:34 p.m. that evening, and the Coast Guard confirmed no further unusual activity afterward.

Japan’s Foreign Ministry lodged formal protests through two channels the same day. Masaaki Kanai, director-general of the ministry’s Asian and Oceanian Affairs Bureau, protested to Sang-yeol Lee, deputy chief of mission at the South Korean Embassy in Tokyo. Separately, Kazuo Nakajo, deputy chief of mission at the Japanese Embassy in Seoul, raised the issue with Min-kyung Lee, director-general of the Asia-Pacific bureau at South Korea’s Ministry of Foreign Affairs.

South Korea rejected Japan’s protest. Its Ministry of Foreign Affairs said the survey was legitimate under international and domestic law and reaffirmed its position that the islets, known as Dokdo in South Korea, are its sovereign territory. “Japan filed an issue with an activity that is legitimate under international and domestic laws,” the ministry said, adding that Japan’s objections had been rejected through diplomatic channels.

The August 7 sighting was not an isolated case. South Korean research vessels conducted similar unauthorized survey activity in the same waters three times in June 2026 alone, each prompting a separate protest from Japan’s Foreign Ministry, and a further instance was recorded in May 2026. Japan’s Foreign Ministry and Coast Guard have logged a recurring pattern of these incidents dating back years, including episodes in 2022 involving the South Korean research vessel Hae Yang 2000, which was also observed trailing wire-like equipment north of Takeshima. In one 2022 case, the Coast Guard asked the vessel’s crew what they were doing, but the ship declined to answer, citing South Korea’s claim of sovereignty over the islets.

Takeshima, a small island group in the Sea of Japan controlled by South Korea and referred to there as Dokdo, has been administered by Seoul since the early 1950s. Japan disputes that control and claims sovereignty over the islets, making them one of the longest-running points of friction between the two U.S. treaty allies. Japan’s exclusive economic zone claim around Takeshima overlaps with waters South Korea also claims, and the two countries’ boundary in the area remains contested rather than formally delimited, which is why Japan characterizes vessel movements there in terms of a “geographic midline” rather than an agreed maritime border.