US Secretary of Defence Chuck Hagel

US Secretary of Defence Chuck Hagel Photo: AP

Washington: The United States pledged support for ally Japan on Wednesday in a growing dispute with China over islands in the East China Sea and senior US administration officials accused Beijing of behaviour that had unsettled its neighbours.

US Defence Secretary Chuck Hagel assured his Japanese counterpart in a phone call that the two nations' defense pact covers the small islands where China established a new airspace defence zone last week and commended Tokyo "for exercising appropriate restraint," a Pentagon spokesman said.

China's declaration raised the stakes in a territorial standoff between Beijing and Tokyo over the area, which includes the tiny uninhabited islands known as the Senkaku in Japan and the Diaoyu in China.

A photo illustration shows a graphic depicting a Chinese national flag flying atop of the disputed islands, called Senkaku by Japan and Diaoyu by China, being seen on the front page of Chinese search engine website Baidu, on a computer screen in Beijing.

Graphic depicting a Chinese national flag flying atop of the disputed islands on the front page of Chinese search engine website Baidu. Photo: Reuters

The United States defied China's demand that airplanes flying near the islands identify themselves to Chinese authorities, flying two unarmed B-52 bombers over the islands on Tuesday without informing Beijing.

It was a sharp reminder to China that the United States still maintains a large military presence in the region despite concerns among US allies that President Barack Obama's "pivot to Asia" strategy has borne little fruit.

In a previously announced trip, Vice President Joe Biden will visit China, Japan and South Korea next week. He will seek to ease tensions heightened by China's declaration, senior administration officials said.

A double page advertisement regarding the territorial dispute between China and Japan over the uninhabited group of islands in the East China Sea -- known as the Senkaku in Japan and Diaoyu in China.

A double page advertisement regarding the territorial dispute between China and Japan over the uninhabited group of islands in the East China Sea -- known as the Senkaku in Japan and Diaoyu in China. Photo: Reuters

Washington does not take a position on the sovereignty of the islands but recognises that Tokyo has administrative control over them and the United States is therefore bound to defend Japan in the event of an armed conflict.

Some experts say the Chinese move was aimed at eroding Tokyo's claim to administrative control over the area.

China's defence ministry said it had monitored the US bombers on Tuesday. A Pentagon spokesman said the planes had not been observed or contacted by Chinese aircraft.

The disputed islands known as Senkaku in Japan and Diaoyu in China in the East China Sea.

The disputed islands known as Senkaku in Japan and Diaoyu in China in the East China Sea. Photo: Reuters

'Friction And Uncertainty'

In a conference calls with reporters, senior US administration officials said China's declaration raised serious concerns about its intentions.

"It causes friction and uncertainty, it constitutes a unilateral change to the status quo in the region, a region that's already fraught. And it increases the risk of miscalculation and accidents," one of the officials said.

China's declaration of a defence zone affects not only Japan but aircraft from other countries throughout the world that routinely fly over the area, the official said.

Mr Biden will raise the issue of the defence zone directly with policy makers in Beijing, the official said. "It also allows the vice president to make the broader point that there's an emerging pattern of behaviour that is unsettling to China's own neighbours."

The official said it raised questions about "how China operates in international space and how China deals with areas of disagreement with its neighbours."

The Pentagon signalled that more military flights into the defence zone claimed by China can be expected.

Colonel Steve Warren, a Pentagon spokesman, told Reuters: "We'll continue to conduct operations in the region, as we have" in the past. He declined to offer details on timing.

The US State Department said it was still trying to determine whether the new defence zone rules applied to civil and commercial aircraft and it told US airlines to take steps to operate safely over the East China Sea.

In addition to the US B-52 flights on Tuesday, flights of Japan's main airline similarly ignored Chinese authorities while flying through the zone.

Japan Airlines and ANA Holdings said they had stopped giving flight plans and other information to Chinese authorities following a request from the Japanese government.

Both said they had not experienced any problems when passing through the zone. Japan's aviation industry association said it had concluded there was no threat to passenger safety by ignoring the Chinese demands, JAL said.

Reuters