Three days after China announced the setting up of an Air Defence Identification Zone (ADIZ) to bolster its claims over parts of the disputed East China Sea, a persisting lack of clarity about how Beijing plans to enforce its control over the contested area has risked fuelling regional tensions, analysts say.

While China has said that aircraft that enter the ADIZ without notifying authorities may risk facing interception from defence forces, two American B-52 bombers were, on Tuesday, allowed to pass through the region, flying within the ADIZ for close to two and a half hours without interference.

Chinese officials on Wednesday confirmed that two aircraft had flown through the eastern rim of the ADIZ. Defence Ministry spokesperson Geng Yangsheng told reporters Chinese armed forces had "monitored the entire process".

Yet it remains unclear whether "identification" by armed forces is the only action China intends to take when aircraft enter the zone.

Foreign Ministry spokesperson Qin Gang told reporters that "different and corresponding measures" would be employed for "different occasions".

Diplomats from three countries said the Saturday announcement by China came as a surprise, suggesting that Beijing may have been better served by bringing countries in the region on board first before rolling out its plan. Failure to do so, coupled with persisting ambiguity about China's plans to enforce its claims, had needlessly stirred regional anxieties, they suggested.

Mr. Qin of the Foreign Ministry said "relevant countries" had been notified before Saturday's announcement, although he declined to name them.

But sources said countries such as South Korea and Japan were told only a few hours before the formal announcement on Saturday morning.

Japan, which is involved in territorial disputes with China over the Senkaku or Diaoyu islands in the East China Sea - the islands lie within both countries' air defence zones, which are overlapping - has warned that the move could result in "unexpected" incidents. Both countries have already had run-ins between naval vessels, while Japan recently scrambled fighter jets and threatened to shoot down a Chinese Unmanned Aerial Vehicle.

The U.S., for its part, has made clear that its aircraft will not follow China's demands, and will only adhere to its own regulations which state that aircraft only need to notify countries if they are heading towards their airspace, not when they are merely transiting through such zones.

Even South Korea, which has recently enjoyed warming ties with China, has expressed "regret" and concern over the move, as the ADIZ also overlaps with its own air defence zone.

Rory Medcalf, Director of the International Security Program at the Lowy Institute for International Policy, said the move would likely make tensions over the disputed East China Sea islands "even harder to manage".

"An ADIZ is not a provocative or negative step in itself; indeed, it can be in the interests of stability and security of the nation enforcing it," he wrote in an article posted on the institute's website, pointing that the U.S., Japan and South Korea had already set up similar zones.

"If China’s new zone did not include disputed maritime territory, if its requirements for compliance applied only to aircraft heading into Chinese airspace, and if neighbours like Japan and South Korea had been consulted ahead of the announcement, then there would be little or nothing for others to object to," he added. Instead, the move was "a unilateral step, announced suddenly and apparently without consultation with two countries whose civilian and military aircraft will be most affected, the US and Japan."

On Wednesday, the question remained as to why Beijing even took the step of risking fanning regional tensions with the announcement if it planned to only "identify" aircraft and not intercept them - as it did to the two B-52s on Tuesday.

In fact, the move comes at a time when the new Chinese leadership has launched a charm offensive to bolster ties with neighbours and tone down tensions over the South China Sea, where China has, in recent years, had run-ins with vessels from Vietnam and the Philippines.

President Xi Jinping and Premier Li Keqiang recently travelled to Southeast Asia promising to expand trade and investment, and reached an agreement with Vietnam on joint exploration in the South China Sea, which is contested by more than 10 countries.

Mr. Qin said China may also consider setting up similar air defence zones to fortify its other frontiers after "completing preparations". This could, analysts suggested, include parts of the South China Sea.

Such a move would be certain to inflame tensions.

As air defence zones generally extend beyond a country's territory into international airspace, it is less likely that China will take the more provocative step of setting up such a zone across its western or northern frontiers, where it shares land borders with India, Russia and a number of Central Asian countries.

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