"This will raise regional tensions and increase the risk of miscalculation, confrontation and accidents," she told reporters.
China said Saturday that all aircraft entering the new air defense zone must notify Chinese authorities and are subject to emergency military measures if they do not identify themselves or obey Beijing's orders. U.S. officials, however, said they have received no reaction to the bomber flights from the Chinese.
The bomber mission underscores Washington's immediate rejection of China's new rules. The U.S., which has hundreds of military aircraft based in the region, has said it has zero intention of complying. Japan likewise has called the zone invalid, unenforceable and dangerous, while Taiwan and South Korea, both close to the U.S., also rejected it.
White House spokesman Josh Earnest would not specifically comment Tuesday on the military flights. "It continues to be our view that the policy announced by the Chinese over weekend is unnecessarily inflammatory and has a destabilizing impact on the region," he told reporters traveling with Obama in Los Angeles.
The U.S. mission took place between about midnight Monday and 3 a.m. EST, said the officials, who requested anonymity because they were not authorized to speak by name about the flights. The flights were first reported by The Wall Street Journal.
China's move to further assert its territorial claims over the islands is not expected to immediately spark confrontations with foreign aircraft. Yet it fits a pattern of putting teeth behind China's claims and could potentially lead to dangerous encounters depending on how vigorously China enforces it and how cautious it is when intercepting aircraft from Japan, the U.S. and other countries.
While enforcement is expected to start slowly, Beijing has a record of playing the long game, and analysts say they anticipate a gradual scaling-up of activity.
The declaration seems to have flopped as a foreign policy gambit. Analysts say Beijing may have miscalculated the forcefulness and speed with which its neighbors rejected its demands.
At least in the short term, the move undermines Beijing's drive for regional influence, said Bonnie Glaser, an Asia expert at the Center for Strategic and International Studies in Washington.
"It doesn't serve Chinese interests to have tensions with so many neighbors simultaneously," she said.
Denny Roy, a security expert at the East-West Center in Hawaii, said China's enforcement will likely be mostly rhetorical at first.
"The Chinese can now start counting and reporting what they call Japanese violations, while arguing that the Chinese side has shown great restraint by not exercising what they will call China's right to shoot, and arguing further that China cannot be so patient indefinitely," Roy said.
China also faces practical difficulties deriving from gaps in its air-to-air refueling and early warning and control capabilities, presenting challenges in both detecting foreign aircraft and keeping its planes in the air, according to Greg Waldron, Asia managing editor at Flightglobal magazine in Singapore.
Despite that, Beijing has shown no sign of backing down, just as it has continued to aggressively enforce its island claims in the South China Sea over the strong protests from its neighbors.
Tensions remain high with Tokyo over islands in the East China Sea called Senkaku by Japan and Daioyu by China. Beijing was incensed by Japan's September 2012 move to nationalize the chain, and Diaoyutai by Taiwan, which also claims them.
Since then, Chinese and Japanese coast guard ships have regularly confronted each other in surrounding waters. Japan further angered Beijing last month by threatening to shoot down unmanned Chinese drones that Beijing says it plans to send on surveillance missions over the islands.
Beijing's move was greeted rapturously by hardline Chinese nationalists, underscoring Beijing's need to assuage the most vocal facet of domestic public opinion. Strategically, it also serves to keep the island controversy alive in service of Beijing's goal of forcing Tokyo to accept that the islands are in dispute a possible first step to joint administration or unilateral Chinese control over them.
Beijing was also responding in kind to Japan's strict enforcement of its own air defense zone in the East China Sea, said Dennis Blasko, an Asia analyst at think tank CNA's China Security Affairs Group and a former Army attache in Beijing.
The Japanese zone, in place since the 1960s, overlaps extensively with the newly announced Chinese zone. Japan, which keeps a public record of all foreign incursions into its zone, actually extended it westward by 14 miles in May.
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Bodeen reported from Beijing. Associated Press writers Jim Kuhnhenn and Matthew Pennington contributed to this report.
