This 2011 photo shows a P-3C patrol plane of Japanese Maritime Self-Defense Force flying over the disputed islets in the East China Sea. (Japan Pool/AFP/Getty Images)

China said Thursday that it had sent warplanes to patrol its newly declared maritime air defense identification zone, as a dispute over an island chain ratcheted up into a dangerous regional standoff.

The move came after Japan and South Korea said Thursday that they had sent surveillance aircraft of their own into the area in the East China Sea. The United States has joined many of China’s neighbors in condemning the decision last week to establish the zone and defied Beijing by flying two B-52 bombers through the area Tuesday.

A Chinese air force spokesman, Col. Shen Jinke, said several fighter jets and an early-warning aircraft had been sent on “defensive” air patrols in the zone to “strengthen the monitoring of aerial targets,” following an earlier patrol shortly after the zone was announced, the official Xinhua News Agency reported.

Establishing the zone Saturday, China had warned that any non­commercial aircraft entering it without notice could face “defensive emergency measures.” Concern immediately surfaced because the zone overlapped similar zones operated by Japan and South Korea, encompassing islands controlled by those countries but claimed by China.

But in a sign of the mixed signals emanating from Beijing this week, a Defense Ministry spokesman said in response to a question that it was “incorrect” to say that countries had the right to shoot down unidentified planes entering air defense identification zones (ADIZs).

Such zones were neither “no-fly zones” nor territorial airspace, Col. Yang Yujun told a news conference, but simply meant to give nations time to react to possible threats. “The country delimiting the zone has the right to identify and ascertain the intentions and attributes of aircraft from foreign countries and make the relevant response according to different situations and degree of threats.”

Experts say China’s decision to establish the zone, apparently imposed unilaterally, inflamed an already tense situation and raised the possibility of military conflict. The latest flights intensify the game of dare being played above Asia’s contested maritime territory.

“Thus far, Beijing has defined its new ADIZ in a categorical manner that ignores the complexities and risks involved,” said Andrew Erickson, an associate professor at the U.S. Naval War College.

“It is to be hoped that Beijing will choose to exercise restraint and allay concerns by its neighbors and other users of the international airspace in question by offering specific clarifications and reassurances,” Erickson said. “Otherwise, suspicions will grow that the ‘new type of great power relations’ Beijing promotes is merely intended to signal that others should yield to a rising China’s principled positions.”

Analysts said China had established the zone to bolster its claims to a chain of tiny, rocky islands administered by Japan, to strengthen its hand in any future negotiations and to match its rival’s own air defense identification zone, established in 1969. In Beijing, it was also seen as a response to Japan’s threat, made in September, to shoot down any Chinese drones that flew above the disputed islands on mapping missions.

Yang, the Defense Ministry spokesman, criticized Japan for its decision to purchase several of the disputed islets from a private landowner last year and complained that its warships had also interrupted Chinese military maneuvers in international waters in October. “So who is changing the status quo unilaterally? Who intensified tensions in the region? Who intensified contradictions unceasingly? And who is undermining regional security?” he asked.

But experts said China’s decision to establish the zone could have backfired, uniting several of its neighbors in condemnation and providing the United States a perfect opportunity to demonstrate its commitment to ensuring stability in the Asia-Pacific region with its fly-through.

Chris Johnson of the Center for Strategic and International Studies in Washington said Beijing’s muted reaction to the U.S. flights, and the fact that there had apparently been no contact with Japanese or South Korean planes this week, suggested that China might not enforce the zone as aggressively as first feared, although that might not go down well at home. “I wonder if they haven’t backed themselves into a little bit of a corner,” he said.

Announcing the zone unilaterally — and using relatively threatening language — had turned out to be something of a public relations disaster for President Xi Jinping’s government, which is usually more sure-footed, he said. “The rollout was terrible,” he added.

On Tuesday, Beijing reacted calmly to the U.S. challenge, simply noting that it had identified and monitored the American warplanes. That response drew criticism from citizens on Chinese micro-blogging sites, and even from state news media.

The nationalist Global Times newspaper said that the United States had engaged China in a “war of public opinion” and that Beijing had “failed to make a timely and ideal response.”

“Beijing needs to reform its information release mechanism to win the psychological battles waged by Washington and Tokyo,” the paper said in an editorial.

Spokesman Shen said the Chinese air force would remain on high alert and would take “relevant measures according to different air threats” to defend the country’s airspace, Xinhua reported.

In another editorial, the Global Times said Japan, not the United States, was the target of the new zone and suggested that enforcement of the zone would be selective.

“If the U.S. does not go too far, we will not target it in safeguarding our air defense zone,” the newspaper wrote. “What we should do at present is to firmly counter provocative actions from Japan.”

A spokesman for the Japanese government said Thursday that its Lockheed Martin-made turbo­prop patrol planes have been conducting routine flights in China’s air defense identification zone since Beijing’s declaration. The spokesman did not say specifically when the flights have taken place or how many there have been. Japan has not been notifying China of its activities.

“We have no particular comment beyond saying that the Japanese government will continue to operate according to the existing policy of protecting its territory calmly and firmly and it will maintain its surveillance and reconnaissance activities,” said Masaru Sato, a Japanese Foreign Ministry spokesman.

Japan’s Defense Ministry did not confirm the flights, but one official, requesting anonymity to describe the situation, said that Japan is “conducting the same monitoring activity as before, and we will not change or restrict such activities.”

China and Japan remain key trade partners and their governments have a strong incentive to avoid armed conflict, but they also have to cater to powerful nationalist audiences at home — making the management of this dispute a delicate balancing act.

South Korea’s flight took place Wednesday near the area of a South Korean maritime research center, built atop a submerged rock that Seoul and Beijing contest.

The flight marks a “clear sign that Seoul will not recognize the new airspace claim,” South Korea’s Yonhap news agency said in its report. Yonhap also reported Thursday that China had rejected Seoul’s request to redraw its air defense identification zone and eliminate an overlap with the zone of South Korea. The South in turn said it may expand its own zone.

In Asia’s waters, territorial disputes go back decades or centuries and draw in nearly every nation in the region. China has clashed in the South China Sea with Vietnam and the Philippines. In the East China Sea, the nastiest dispute of late has been between Japan and China over several uninhabited islets and rocks known as the Senkaku in Japanese and the Diaoyu in Chinese. Since the Japanese purchase of the islets last year, China has increased its surveillance — both with vessels and aircraft — in the area, and Japan has frequently scrambled its own fighter jets in response.

U.S. officials said China’s air defense identification zone needlessly raised tensions between Asia’s two largest economies. In his trip next week through the region, Vice President Biden plans to convey those concerns to China, a senior Obama administration official told reporters Wednesday.

“There is an emerging pattern of behavior by China that is unsettling to China’s own neighbors,” the official said. Biden will raise questions “about how China operates in international space and how China deals with areas of disagreement with its neighbors.”

Harlan reported from Seoul. Li Qi contributed to this report.