TOKYO/SEOUL (Reuters) - Japan on Wednesday (Jan 25) lodged a protest with South Korea after a South Korean official visited a group of islets claimed by both countries, putting more strain on ties already damaged by the legacy of Japan's 1910-1945 rule of Korea.

The islands that lie equidistant between the two countries are called Takeshima in Japanese and Dokdo in Korean. They are controlled by South Korea and also claimed by Japan, a long-running irritant in their relations.

Kim Kwan Yong, the governor of South Korea's Gyeongsangbuk-do Province, visited the islands early on Wednesday, "to see for himself the security conditions and to encourage the Dokdo guards", his office said in a statement.

Japan denounced the visit. "This is totally unacceptable in light of our country's stance regarding the sovereignty over Takeshima," Chief Cabinet Secretary Yoshihide Suga told a regular news conference.

"It is extremely regrettable that the visit was carried out despite our advance protests and calls for suspension. We promptly lodged a stern protest against the South Korean government and demanded prevention of recurrence."

In 2012, South Korea's then-president, Lee Myung Bak, became the first leader of his country to visit the islands.

Ties between the two counties have been plagued for decades by the legacy of Japan's occupation of the Korean peninsula and the issue of "comfort women", as those forced to work in Japanese wartime military brothels are known.

The latest flare-up in tension comes after Japan recalled its ambassador to South Korea over a statue commemorating Korean"comfort women", put up near the Japanese consulate in the South Korean city of Busan last year.

Japanese Foreign Minister Fumio Kishida last week denounced as "unacceptable" a reference to the islands as South Korea's"easternmost territory", on a website set up for the 2018 winter Olympics, being held in South Korea.

"Dokdo holds a special place in the hearts of Koreans," the website says.