Members of S.Korean Marine Corps take part in a military exercise in remote islands called Dokdo in Korean and Takeshima in Japanese, South Korea. File photo/ Reuters

A group of South Korean lawmakers visited islands disputed with Japan, sparking a protest from the Japanese foreign ministry as the countries' already tense relationship deteriorates further.

Six Korean lawmakers on Saturday flew to the islets, known as Dokdo in Korea and Takeshima in Japan, in part to protest Japanese curbs on shipments of essential components for making smartphone chips, South Korea's chief export.

“Regardless of the South Korean government's efforts, Japan has not only dropped South Korea from the “white list,” but also, it is claiming Dokdo as part of its territory, worsening the South Korea-Japan relations,” said Sul Hoon, a ruling Democratic Party lawmaker.

Japan's foreign ministry has lodged a “stern” protest over the visit. In its statement, the ministry said the Korean lawmakers had ignored Japan's previous demand that the plan be scrapped, and called the visit “extremely regrettable.”

The islands are Japan's inherent territory in terms of both history and international law, the ministry said.

Relations between South Korea and Japan are at the lowest in years after a row over compensation for wartime forced labourers during Japan's occupation of Korea until end of World War Two. Ties soured further when Japan removed South Korea from a “white list” of countries with fast-track export status, and Korea followed by scrapping a military intelligence-sharing pact with Japan.

Reuters