Foreign Minister Yoshimasa Hayashi on Tuesday described the four islands as an "integral part" of Japan, the Japanese daily Sankei Shimbun reported.
Previously, Prime Minister Fumio Kishida had also used this wording.
In view of Russia's war of aggression against Ukraine, his government is returning to language that Kishida's predecessor Shinzo Abe had avoided for 10 years in the hope of reaching an agreement with Russia's President Vladimir Putin.
The archipelago, which has been disputed for decades, lies between Russia's Kamchatka Peninsula and Japan's northern main island of Hokkaido.
Japan lost the islands to the Soviet Union after its surrender in World War II.
Tokyo is reclaiming the since-occupied islands of Etorofu, which in Russian is called Iturup; Kunashiri or Kunashir; Shikotan and the Habomai group on the dividing line between the Sea of Okhotsk and the Pacific Ocean.
Proposals to return initially two of the four disputed islands as a kind of interim solution were rejected.
Abe dispensed with the phrase "integral part" of Japan during his years in office in order to signal a more flexible stance in the dispute with Russia in the hope of a historic breakthrough.
Kishida's return to the old language, according to observers, now signals that he is saying goodbye to this hope.
The dispute continues to prevent the conclusion of a peace treaty between the two countries.
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