OVER THE weekend, China abruptly raised the stakes in a long-simmering dispute over Japanese-controlled East China Sea islands in a manner that is worrisome and reckless. China unilaterally announced the imposition of a new “air defense identification zone” over a broad swath of the sea, demanding that planes identify themselves to China and obey its orders or face potential military action. The zone overlaps a similar one maintained by Japan and is nothing less than an assertion of sovereignty.

At issue are a string of uninhabited islands that are claimed by both countries. Last year, Japan bought them from a private owner; China increased the frequency of patrol ships, and Japan responded with patrols of its own. The United States is neutral in the territorial dispute but committed to the defense of Japan, and it has repeatedly urged both Asian powers to negotiate.

The shadow-boxing with sea patrols was already unsettling before the Chinese announcement of the new zone in the air Saturday. China is saying, in effect, that it now controls the zone’s air traffic and could intercept planes that don’t follow its rules. The Chinese action creates a very real hazard of accident or error leading to open hostilities, which could draw in the United States through its commitment to Japan. Both Secretary of State John F. Kerry and Defense Secretary Chuck Hagel were right to immediately protest China’s action. Japan also called on China to step back. But Beijing has stood fast.

Some years ago, its leaders reassured the world that a rising economic superpower did not mean a more muscular China, in the region or beyond it. They called it “China’s peaceful rise.” The weekend’s announcement looks to be anything but. It is true that China’s territorial claim to the islands is long-standing. But to suddenly impose restrictions on air travel over such a wide territory is not a “peaceful rise” nor the sign of a willingness to negotiate. China claims another expansive territory in the South China Sea that has brought it in conflict with its neighbors there. If this air zone is allowed to stand, it may encourage China to step up the pressure in other ways, too.

Recent months had brought signs of some cooperation and dialogue between the military forces of the United States and China. This remains urgent and important. If China really feels the need for an air identification zone beyond its territorial waters, perhaps it should join with Japan and neighboring states to create a joint zone in which they share aviation data and agree to work out claims on the waters and islands below. That may be an optimistic goal, but China must realize that unilaterally grabbing control of the skies is not a path to tranquillity.