China said Wednesday that it has observed the US B-52 bombers flying in its newly established Air Defense Identification Zone (ADIZ) over the East China Sea, asserting that it is capable of exercising effective control over the airspace.

The unarmed bombers flew from Guam to China's ADIZ on a scheduled training mission and didn't encounter any Chinese planes, Pentagon spokesman Colonel Steve Warren told reporters Tuesday.

"We have continued to follow our normal procedures, which include not filing flight plans, not radioing ahead and not registering our frequencies," Warren said, according to Reuters.

In a statement posted on the website of China's defense ministry on Wednesday, the ministry's spokesperson Geng Yansheng said the US aircraft flew south and north along the eastern border of the zone from 11 am to 1:22 pm on Tuesday, about 200 kilometers to the east of the Diaoyu Islands, which are at the center of a territorial dispute between China and Japan.

The Chinese army has monitored the whole process, conducted identification in a timely manner and ascertained the aircraft's type, Geng said.

"China is capable of exercising effective control over this airspace," Geng added.

The defiant move from the US came after its opposition against China's establishment of the zone over the past weekend, which demands any aircraft flying in the zone to provide its flight plan to the Chinese side.

With the timing of this flight, the US has made very clear its defiance to not accept the ADIZ established by China, an air force expert, who requested anonymity, told the Global Times on Wednesday.

The move also symbolizes US support for Japan, with which Washington has a security pact, said analysts.

The US Ambassador to Japan, Caroline Kennedy, said Wednesday, "The Japanese can see every day that America is here for them as a partner in the defense of Japan."

However, the air force expert noted the US wouldn't go too far in contesting China, given the fact that the B-52s were on an unarmed training mission. "It sends a signal to Japan that it doesn't want to see the conflict escalate and hence Japan should not step too much across the line," he added.

The US defiance aroused anger among Chinese Web users on Sina Weibo, with many of them calling for the government to act more aggressively.

"We need to take a rational attitude as the ADIZ emphasizes identification and is not an operational zone," the expert said, noting that it won't be the last time that US aircraft enter the zone.

China has warned that those who do not comply with its rules about the ADIZ can face "defensive emergency measures," but didn't specify what the measures would be.

Asked whether Tuesday's reaction toward the US bombers would be the same for other foreign planes entering the ADIZ without notification, foreign ministry spokesperson Qin Gang told a press briefing Wednesday that for any similar cases in the future, China would "make an appropriate response" that depended on the "situation and degree of threat."

China needs to deliver a more explicit message regarding its position on the zone to the US and the current conflict is better addressed through diplomatic negotiations rather than any other means, said Jia Qingguo, an associate dean of the School of International Studies at Peking University.

Following China's establishment of the ADIZ, the Japanese defense ministry proposed expanding its similar zone to the Ogasawara Islands, some 1,000 kilometers south of Tokyo, and the proposal has entered discussions about its implementation, Japan's Yomiuri Shimbun paper reported on Wednesday.

"Japan wants to take the opportunity to expand its military presence and assert its control of the islands," the military expert said.

At the request of the Japanese government, Japan Airlines and ANA Holdings said they stopped giving flight plans and other information to Chinese authorities on Wednesday.

Also on Wednesday, Qin, the foreign ministry spokesperson, refuted Australia's criticism of the zone after Australia summoned the Chinese ambassador to ask for an explanation.

"Australia's irresponsible statements on the East China Sea Air Defense Identification Zone are completely mistaken, China cannot accept them," he said in a statement.

Qin said that China had "expressed its strong dissatisfaction" and called on Australia to "immediately correct its mistake, so as to avoid damaging China-Australia relations."

Agencies contributed to this story

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