South Korea denounced Japan Tuesday for again laying claim to its easternmost islets of Dokdo, saying the move undermines Seoul's efforts to improve their long-strained ties.
  

Japan's defense ministry released its annual defense white paper earlier in the day with references to Dokdo and the Russian-controlled Kuril Islands as Japanese "sovereign territory."
  

Dokdo, which lies closer to South Korea in the body of water between the Korean Peninsula and Japan, has long been a source of tension between the neighbors along with other issues stemming from Japan's 1910-45 colonial rule of Korea. South Korea has kept a small police detachment on the islets since 1954.
  

"The territorial issue over our sovereign territory of the Northern Territories and Takeshima still remains unresolved," the paper said, using the Japanese names for the Kuril Islands and Dokdo.
  

It is the 11th straight year the annual paper has included such claims together with maps marking Dokdo as Japanese territory.
  

Shortly after the report's release, South Korea's defense ministry called in Army Col. Nobuhisa Goto, a defense attache at the Japanese Embassy in Seoul, to lodge a protest with the Japanese government.
  

"The Ministry of National Defense of the Republic of Korea strongly remonstrates about the 2015 defense white paper which projected our own territory of Dokdo as Japan's territory and marked it as part of Japan's domain on the related map while also drawing an unagreed-upon line for the Exclusive Economic Zone there," the ministry said in a statement.
  

It "resolutely urges prompt action to correct them and measures not to repeat such unjust behavior," it added.
  

The Foreign Ministry also issued a statement denouncing the latest report as a "provocation" in the year the two countries mark the 50th anniversary of the normalization of bilateral ties.
  

The renewed claim amounts to "an act denying the history of invasion of the Korean Peninsula of Japan's past imperialism" and Tokyo's own admission that it has an incorrect perception of history, the statement said.
  

"Our government will respond firmly to any provocation by Japan with regard to Dokdo, which is clearly our sovereign territory historically, geographically and under international law," it said.
  

The ministry delivered its own protest to Kenji Kanasugi, a minister at the Japanese Embassy, after calling him in to meet with Lee Sang-deok, director-general of the Northeast Asian affairs bureau.
  

During the meeting, Lee demanded the Japanese government delete the references to Dokdo from the white paper and prevent similar actions in the future, according to a ministry official who spoke on condition of anonymity.
  

"(He) pointed out that continuing such actions is of no help to South Korea-Japan relations at an important time when we are working to improve bilateral ties and called for Japan's prudent response," the official said.
  

Tensions between the two countries have eased somewhat in recent weeks, spurring speculation of a trilateral summit with China in the coming months.
  

Last month, Foreign Minister Yun Byung-se visited Tokyo to mark the 50-year anniversary and hold talks with his Japanese counterpart, Fumio Kishida. It was the first visit to Japan by Seoul's top diplomat in more than four years.
  

Earlier this month, Japan listed a package of early industrial sites as UNESCO world heritage after accepting South Korea's demand that it acknowledge its use of Korean slave labor at some of them. (Yonhap)