TOKYO—In a move that would be sure to heighten tensions between Japan and China, metropolitan Tokyo plans to buy a group of islands at the center of a bitter territorial dispute, its combative governor declared Monday.

Shintaro Ishihara, known for his nationalistic views and provocative style, said the metropolitan government has been negotiating with the private Japanese owner of the islands—known as the Senkaku in Japanese and the Diaoyu in Chinese—and that he hopes to seal a deal by the end of the year. He didn't mention a price.

Both Japan and China claim the islands, located in the East China Sea between Japan's southern Okinawa Prefecture and Taiwan. In one recent flareup of the simmering dispute, a September 2010 collision between a Chinese fishing boat and a Japanese coast guard vessel near the islands set off a diplomatic war of words and dueling nationalist protest marches.

"Tokyo has decided to buy the Senkaku Islands. Tokyo is going to protect the Senkakus," Mr. Ishihara said in a speech in Washington at the Heritage Foundation, a conservative think tank. "Would anyone have a problem with an act by the Japanese to protect our own land?" The purchase, he said, would aim to prevent China from taking "effective control" out of Japan's hands.

Foreign Minister Koichiro Gemba declined to comment specifically about Mr. Ishihara's remarks, saying he hasn't confirmed the details. He then repeated Japan's official stance: "It's an unquestionable fact that the Senkaku Islands are Japan's unique territory both from historical and legal perspectives. All I can say is we continue to control them effectively." Japan counts them as part of the southwestern prefecture of Okinawa