Japan lodged a protest with South Korea over military drills it conducted on disputed islands, saying it was "extremely regrettable", the foreign ministry said in a statement issued on Friday.
The foreign ministry said it summoned a senior diplomat at the South Korean embassy in Tokyo, and the Japanese embassy in Seoul also summoned a senior South Korea official to make the protest.
"Takeshima is indisputably an inherent territory of Japan, in light of historical facts and based on international law," the ministry said in the statement.
"The drills by the South Korean military are unacceptable and extremely regrettable."
The two nations have long been at loggerheads over the sovereignty of the group of islets called Takeshima in Japan and Dokdo in Korea, which lie about halfway between the East Asian neighbours in the Sea of Japan, also known as the East Sea.
"The East Sea territory defence exercise was carried out to conduct our mission to protect our territory, people and property," a South Korean military official said.
The South Korean military has conducted the military drill routinely every year, the official added.
