TOKYO (Kyodo) -- Japan made an explicit claim to ownership of a group of Russian-held islands off Hokkaido in an annual foreign policy report released Tuesday, after refraining from doing so last year amid hopes of breaking a deadlock in the territorial spat.
The dispute has prevented the two countries from signing a World War II peace treaty even 75 years after the end of the conflict.
In the 2020 edition of its Diplomatic Bluebook, the Foreign Ministry also pointed to Japan's heightened tensions with South Korea over trade controls and compensation for wartime labor, and condemned North Korea for continuing its ballistic missile tests in defiance of U.N. resolutions.
The report said the islands, which Japan calls its Northern Territories and Russia calls the Southern Kurils, are "under the sovereignty of Japan."
It said the dispute over the islands, lying off Japan's northernmost main island of Hokkaido and straddling the Pacific Ocean and Sea of Okhotsk, is a matter of the "greatest concern," and that efforts to reach an agreement would continue.
The Soviet Union seized the islands following Japan's surrender in 1945, which Moscow maintains was a legitimate outcome of the war. Tokyo argues the acquisition was illegal and has continued to demand their return.
The 2018 edition of the report stated "the Four Northern Islands belong to Japan" but when the 2019 edition was released last April, the wording had disappeared.
At the time, Prime Minister Shinzo Abe was hoping to convince Russian President Vladimir Putin to agree to return some of the islands -- Shikotan and the Habomai islet group -- an aspiration mentioned in a 1956 joint declaration.
The declaration ended the state of war between the two countries and kept the path open to one day signing a peace treaty. The other islands are Etorofu and Kunashiri.
But when the leaders met in June on the sidelines of a Group of 20 summit in Osaka, no such deal was made, and a peace treaty looked as remote as ever.
The 2020 edition of the Diplomatic Bluebook describes South Korea as an "important neighbor" of Japan but said bilateral relations remain in a "severe situation" amid disputes over a long list of issues.
The countries have been at odds since South Korea's top court in 2018 ordered payment for people deemed to have been forced to work in Japanese factories during the 1910-1945 period of colonial rule on the Korean Peninsula.
Tokyo's move last July to tighten regulations on the export to South Korea of key materials for the manufacture of semiconductors and display panels drew complaints that this was in retaliation for the court decision.
Seoul struck back by announcing the termination of a bilateral military intelligence-sharing pact, but later suspended its decision.
Meanwhile, the report said North Korea's repeated ballistic missile tests "pose a serious threat not only to Japan but the entire international community" and are "completely unacceptable," expressing support for the now-stalled denuclearization talks between Pyongyang and Washington.
It also touched on Japan's response to the global coronavirus pandemic, including evacuating citizens from Wuhan in central China, where the outbreak was first discovered.
Japan continues to be in favor of Taiwan's participation as an observer at the World Health Assembly, the report said. Beijing has blocked Taiwan from attending the annual meeting of the World Health Organization's decision-making body since 2017.
Regarding a section of the policy report that described a South Korea-controlled pair of islets in the Sea of Japan as an inherent part of Japanese territory, the country's Foreign Ministry on Tuesday summoned a senior Japanese embassy official in Seoul and lodged a protest, according to Yonhap News Agency.
Japan lays claims to the rocky outcroppings, which South Korea took effective control of in 1954. The islets are known as Takeshima in Japan and Dokdo in South Korea.
The policy report says South Korea has illegally occupied the islets despite having no international legal basis.
The ministry, in a commentary issued Tuesday, said the islets are "clearly an integral part" of South Korea and demanded an immediate withdrawal of Japan's "unjust claims" to the islets.