South Korea is closely watching Japan's plans to unveil the results of its review of textbooks for middle school students as they are expected to contain Tokyo's repeated claim to South Korea's easternmost islets of Dokdo, officials said Monday.



Later in the day, Japan is set to make public the outcome of an examination of school textbooks that will likely include Tokyo's territorial claim to Dokdo, in what could be another source of tension between the two historical rivals.



Japan has long declared sovereignty over the Dokdo islets, which lie closer to South Korea than Japan in waters between the two countries, in one of the thorniest diplomatic issues between the two.



All of the 18 textbooks will likely state the islets are Japan's territory in line with newly revised teaching manuals for Japanese textbooks for middle and high school students, according to officials. The new guidelines were unveiled in January 2014.



On Tuesday, Japan also plans to unveil its 2015 diplomatic paper, named the Diplomatic Bluebook, which will reportedly repeat its claim to the islets.



In last year's report, Tokyo said the islets are "clearly an inherent territory of Japan," in light of historical facts and based upon international law.



South Korea has vowed to take stern actions against Japan's possible provocations over Dokdo, saying that it is needless to say that the islets are South Korean territory in terms of history, geography and international law.



"Seoul will sternly respond to any provocations that Japan makes in terms of Korea's territorial sovereignty," a Seoul official said.



Experts say that Japan's potential provocations over the islets are expected to further dampen bilateral ties, which have already reached their lowest level in recent years.



This year marks the 50th anniversary of the normalization of the Seoul-Tokyo ties. But their ties have been strained due to history issues that include Tokyo's use of South Korean women as wartime sex slaves in World War II. (Yonhap)