South Korea issued a strong protest Friday after Japan authorized dozens of updated high school textbooks that renew territorial claims to the South's easternmost islets of Dokdo in a move sure to aggravate historical tensions between the two neighbors.

The approval dampened the mood for bilateral cooperation, which has emerged in the wake of the North's latest provocations and a Dec. 28 deal to settle the decades-old issue of Japan's wartime sexual enslavement of Korean women, observers here noted.

Stressing that Dokdo is Korea's inherent territory historically, geographically and by international law, Seoul's Foreign Ministry "strongly deplored" Tokyo's approval of the textbooks and demanded an "immediate" rectification.

"The Japanese government should never forget that teaching correct history is its grave responsibility for its future generations and neighboring countries suffering from Japan's history of invasion," the ministry said in a press release.

"We once again urge Japan to show its efforts to open a new chapter of Korea-Japan relations through sincere action, while squarely facing historical truths."

The ministry called in Hideo Suzuki, a minister at the Japanese Embassy in Seoul, to lodge a protest. Chung Byung-won, director-general handling Northeast Asian affairs at the ministry, met with him.

The authorization of the textbooks to be used from April next year represented a bolstering of Tokyo's claims to Dokdo, because 27 of the newly approved 35 social studies textbooks -- or nearly 80 percent -- claim that the South is "illegally occupying" the islets.

In the previous screening in 2012, 21 of the 39 total textbooks -- or 53.8 percent -- included Tokyo's territorial claim to the islets, called "Takeshima" in Japan.

Many of the updated textbooks state that Dokdo is Japan's "inherent" territory, while some others highlight that the Tokyo government has proposed taking the simmering territorial issue to the International Court of Justice.

South Korea's education ministry also released a statement of protest and denounced Japan's new textbooks as "un-educational."

"Teaching a distorted view of history to students who are yet immature in historical perception and making judgments can lead to a repeated history of aggression, which could jeopardize peace in Northeast Asia," it said.

The education ministry said it will distribute reference materials and textbooks in April, explaining South Korea's position on the issue of Dokdo and emphasizing the description of the islet in new state history textbooks.

It is also planning to send a correction request to Japan's foreign ministry in June.

The issue of Dokdo has been one of the thorniest issues that have fueled historical enmities between the two countries. Korea has been in effective control of the islets with a small police detachment since its liberation from Japan in 1945.

To counter Tokyo's claim to Dokdo, the Foreign Ministry plans to translate its promotional video on Dokdo into 13 additional languages including Vietnamese, Malay, Indonesian, Hungarian and Turkish.

The ministry has already posted the video on its website, dokdo.mofa.go.kr, in 12 languages including English, French, Spanish and Chinese.

All of the six approved history textbooks carry content related to Japan's wartime sexual enslavement of Asian women, euphemistically called comfort women.

But the textbooks stopped short of mentioning explicitly that the victims were forced by Japan to serve at front-line military brothels during World War II. Instead, they said in a vague manner that the victims were "sent" or "mobilized" to work at the comfort stations.

Historians estimate that up to 200,000 women, mainly from Korea, were forced into sexual servitude.

Late last year, Seoul and Tokyo settled the comfort women issue with the latter apologizing for the atrocities and agreeing to provide 1 billion yen (US$8.9 million) for a foundation to be established by South Korea to support the surviving victims.

The implementation of the landmark deal has yet to make any progress, as the victims have refused to accept it. Lambasting it as "diplomatic collusion" between the two governments, the victims argue that the deal was struck without sufficient consultations with them.

The content about the controversial deal was not reflected in the new history textbooks as the publishers' applications for the state authorization process were made before the deal was reached.

Private Japanese publishers must go through an authorization process to get state approval to publish textbooks for use in Japanese schools.

Tokyo says the process, which is conducted every four years, is necessary to ensure the "objectivity and impartiality" of textbooks, but critics here argue it is intended to whitewash and gloss over Japan's colonial-era wrongdoings.

Local civic groups released statements that urged Japan to withdraw its policy of writing distorted history textbooks.

"The Japanese government's conservative swing seems to have been reflected in the textbooks," the Asia Peace and History Education Network said. (Yonhap)