Updated

China responded on Thursday to growing international defiance of its new air-defense zone in the East China Sea both by sending advanced fighter jets to the area and trying to play down any threat of military retaliation—underlining the confusion and escalated tension over territorial disputes in East Asia.

The announcement by China's air force that it had sent fighters and an early warning aircraft to patrol the zone came just a few hours after Japan and South Korea, following the U.S. lead, said their military aircraft had flown into the zone without notifying Beijing over the past few days, and would continue to do so.

The U.S. challenged the zone's credibility on Tuesday by sending in two B-52 bombers without informing Chinese authorities, who had warned when they declared the zone on Saturday that such incursions would be met with unspecified "defensive emergency measures."

The conflicting signals from Beijing highlight the challenge the Chinese leadership faces as it tries to contain the international fallout from its surprise decision to establish the zone, without appearing weak in front of an increasingly nationalistic domestic audience.

China's apparent easing of its original warning suggests its fighters will monitor and escort rather than repel U.S., Japanese and South Korean aircraft that violate the rules of the zone, which covers islands claimed by Beijing and Tokyo, said Chinese and foreign analysts.

But to maintain its credibility internationally and domestically, it is likely to increase such escorts, a move that in such a tense political climate greatly increases the risk of an aerial incident that could spiral into a military clash, analysts and diplomats said.

A defense ministry spokesman said China had "identified" all foreign aircraft entering the Air Defense Identification Zone that was established on Saturday over an area covering islands at the center of a fierce territorial dispute between Tokyo and Beijing.

But Col. Yang Yujun, a defense ministry spokesman, told a monthly news conference that the ADIZ wasn't a no-fly zone or an extension of China's airspace. He said it was "incorrect" to suggest China could shoot down planes in the zone.

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