BEIJING — The new air defense zone declared by China appears to have been approved by President Xi Jinping, the culmination of more than a year of pressure by Beijing to weaken Japan’s grip on disputed islands in the East China Sea, and by extension to expand China’s long-term access to the Western Pacific.

As Mr. Xi amassed power in the past year, he voiced increasing displeasure with Japan, and in a curt, impromptu encounter in St. Petersburg, Russia, in September with the hawkish prime minister, Shinzo Abe, Mr. Xi said Japan must face “history squarely,” according to an account in China’s state-run news media.

Mr. Xi has rebuffed Mr. Abe’s requests for a formal summit meeting, another sign of Mr. Xi’s firm stance on Japan.

Mr. Xi’s position as leader of the Communist Party and chairman of the military commission that runs China’s armed forces made him the primary decision maker on issues like the air defense zone, Chinese experts said. Over the past year, they say, he has been particularly attentive to the East China Sea dispute.