SEOUL—Tokyo recalled its ambassador to Seoul on Friday after South Korea President Lee Myung-bak flew to a pair of small islets also claimed by Japan, in a high-profile assertion of territorial rights.
"Dokdo is truly our territory," Mr. Lee said during the visit, the first by a South Korean president to the territory, known as Takeshima in Japan and as Liancourt Rocks by the U.S. and other parties outside the dispute. He added that it is "worth sacrificing our lives over."
Mr. Lee flew by helicopter and spent a little more than an hour on the one of the pair that is inhabited. He prayed at a small cemetery and drank tea with two people who live on Dokdo for part of the year.
Speaking to a small group of South Korea soldiers stationed there, Mr. Lee said, "Let's be on guard, with pride."
Japanese Prime Minister Yoshihiko Noda said Friday that "the visit is incompatible with Japan's position and therefore unacceptable." It isn't clear for how long Tokyo will recall its ambassador.
The latest tit-for-tat appeared to be prompted by Japan's release last week of a defense white paper restating its claims to the territory, which it calls Takeshima. Tokyo's assertion is an annual ritual that typically provokes criticism from Seoul, followed by a statement reasserting South Korean ownership of the islets.
This time, however, Mr. Lee's office announced Friday morning that he was on his way to Dokdo.
"This has been building for some time," said Lee Chung-min, a former advisor to Mr. Lee who is now a dean at Yonsei University in Seoul. "I think he just got fed up."
The South Korean president—who has just seven months left in his five-year term—has been under pressure lately to act on some historical disputes with Japan, including another one over compensation for Korean women who were forced into sexual slavery for Japanese soldiers during World War II. Two rulings by South Korea's constitutional court over the past year has forced the issue of compensation for victims of the Japanese colonial period.
Mr. Lee began his presidency in 2008 emphasizing what he called a future-oriented relationship with Japan, and advocated low-key diplomacy the historic issues, but the president and his diplomats made little progress with Tokyo over the matters.
President Lee is likely to discuss Dokdo and Korean-Japanese relations in a speech Wednesday, the anniversary of South Korea's liberation from Japan and the end of World War II.
Meanwhile, the dispute also plays out in inter-Korean relations, though Pyongyang uses the dispute over the islets to level criticism at both Seoul and Tokyo. Earlier this week, North Korea's state media criticized Japan's latest white paper, and said Tokyo "regards the islets as a point for launching its reinvasion of Korea."
The islets in question had long belonged to South Korea, according to historical texts in both countries, but became disputed territory after Japan's colonization of the Korean peninsula a century ago.
Mr. Noda said Friday evening in Tokyo that the islets belong to Japan "historically and by international law."
The disputed islets cover an area equal to two or three city blocks and possess little economic value. But politicians in Japan and South Korea occasionally fan the territorial dispute to stoke nationalist sentiment. Otherwise, the two countries enjoy close economic and political relations.
In South Korea, possession of Dokdo is an emotional issue that unites people across the political spectrum. Celebrity activists have purchased advertisements in Times Square in New York and in London's Piccadilly Circus touting South Korea's rights to it.
In late June, South Korean resentment over the colonial-period disputes forced Mr. Lee to scrap signing of an agreement to share some military information with Japan. The pact is similar to one that South Korea has with more than 20 other nations, but critics invoked Japan's history as a former occupier to oppose it.
In Japan, the claim for Takeshima is at the fringes of the country's political discussion and is driven mainly by rightist politicians. They have tried to keep the matter in the spotlight, along with a higher-profile territorial dispute with China over islands in the East China Sea.
Last year, a delegation of Japanese parliamentarians from the main opposition party were blocked from entering South Korea after arriving in Seoul with plans to visit the disputed islets. Earlier in 2011, two lawmakers from Prime Minster Noda's governing party became the first members of the ruling Democratic Party of Japan to attend an event called "Takeshima Day" hosted by Shimane prefecture, which is on Japan's west coast closest to the disputed islets.