BEIJING — Tensions between China and the United States and its Asian allies escalated on Monday as several well-connected Chinese experts immediately criticized an announcement earlier in the day that the United States and Japan had reached a major agreement to deploy a second advanced missile-defense radar on Japanese territory.

The new conflict, coming as China and Japan have been sparring over claims to disputed islands in the sea between them, emerged as Defense Secretary Leon E. Panetta arrived in Beijing from Tokyo to meet this week with China’s leadership, including Xi Jinping, who is expected to become the nation’s next president.

The scheduling of Mr. Panetta’s meeting with Mr. Xi was made public only as the defense secretary flew to Beijing. It suggests that Mr. Xi, currently serving as China’s vice president, has made a recovery from whatever ailment — physical or political — had kept him from making public appearances for two weeks. The absence prompted widespread speculation about whether Mr. Xi would ascend to the top post, as long planned.

Even as the latest controversy erupted, the Chinese government began to reassert control over chaotic anti-Japanese riots that spread over the weekend to dozens of cities. But the anniversary of a 1931 incursion by Japanese troops, generally considered the opening shot in Japan’s occupation of major parts of China from 1931 to 1945, revitalized the protesters angered by a territorial dispute involving islands claimed by Japan and China.