Asked whether Japan might station officials on the islands to defend Japanese territory, Mr. Suga said the move was “one option” under consideration.

“Our country will never make a concession on the matter of sovereignty,” he added.

An effort by either country to forcibly control the islands could lead to an escalation of the conflict, analysts have warned. They also worry that a small, unintended episode at sea as Japanese and Chinese boats chase each other near the islands could lead to a wider conflict. Open hostility between China and Japan, an important American ally in the region, also risks drawing in the United States.

Prime Minister Shinzo Abe of Japan came to power in December on campaign promises that initially included a reference to placing government officials on the islands. But shortly before the voting, Mr. Abe said that he would put off a decision on the matter.

He also did not include that promise in his official campaign platform for separate elections in July. However, a policy document issued by his ruling Liberal Democratic Party around the same time mentions the need for Japanese officials to be based on the island, underscoring the government’s shifting stance.

The territorial dispute, which has lasted for decades, flared last year after the Japanese government bought three of the five islands from their private owner. The move drew outrage from Beijing, which saw it as an effort by Japan to solidify its claims. Japan said at the time that it was acting to pre-empt Japanese nationalists from trying to take more provocative steps to assert control.