The Japanese government says a South Korean research ship has been found conducting what appeared to be a marine survey in Japan's exclusive economic zone south of the Takeshima Islands.

South Korea controls the islands. Japan claims them.

The Japanese Foreign Ministry says the vessel was spotted dropping what looked like a wire into waters in the Sea of Japan area at around 2 p.m. on Thursday. It adds that the South Korean side had not filed any prior application for the activity.

The head of the ministry's Asian and Oceanian Affairs Bureau, Namazu Hiroyuki, summoned a senior diplomat from the South Korean Embassy in Tokyo to protest the ship's actions and call for an immediate halt.

A similar protest was lodged by the Japanese Embassy in Seoul with the South Korean Foreign Ministry.

The Japanese government maintains the islands are an inherent part of Japan's territory. It says South Korea is illegally occupying them.