Top American diplomat John Kerry visits the region this week amid growing US criticisms of China's territorial claims in the disputed East and South China Seas. The Straits Times examines the shifting tone in Washington and its impact in Beijing.
WHEN the United States military flew two B-52 bombers through China's newly declared air defence identification zone (ADIZ) in December, it was meant to warn Beijing to back off from aggressively pressing its territorial claims in the region.
Since then, China's response suggests the US message has not got across.
Last week, the Obama administration moved to harden its stand.
"They were making explicit what has been implicit," said Dr Richard Bush, director of the Centre for East Asia Policy Studies at Brookings Institution.
Officials had previously talked more generally about the need to observe the rule of law in territorial claims and the US commitment to Asia.
But over two consecutive days last week, the US' top diplomat to Asia, Assistant Secretary of State Daniel Russel, was a lot more specific.
Speaking to the foreign press on Wednesday and then to Congress a day later, he said the US believed strongly that China's territorial claims in the South China Sea must be based on land features in accordance with the United Nations Convention on the Law of the Sea.
Speaking to the House Committee on Foreign Affairs, he urged China to "clarify or adjust" its claims in the area to fall in line with international law.
It was the strongest rejection yet from a US official of China's use of a so-called nine-dash line to claim a large chunk of the South China Sea, as a chorus of criticism against the Chinese was building up.
But it was also curious in that it came after the issue appeared to have gone off the boil.
Analysts say the timing of the stronger US line comes down to several factors.
Despite numerous statements in December by US officials calling on China to not implement its zone and refrain from starting new ones, a recent report by Asahi Shimbun said that Beijing had drafted plans for a zone that covered the South China Sea.
Another reason might be the desire to set some boundaries ahead of high-profile visits by US leaders to the region.
Secretary of State John Kerry will visit China this week as part of a four-nation trip to Asia while President Barack Obama is tipped to make two separate trips to Asia this year.
"I think the administration was getting very strong feedback from its South-east Asian friends and their own intelligence that the Chinese were developing a perception that the US was going to be distracted and (it) would not be as strong on these issues," said Mr Ernie Bower, senior adviser for South-east Asia studies at the Centre for Strategic and International Studies.
"There was a real feeling that China read that it had been very successful in its ADIZ in Japan and a new ADIZ might be coming up in the South China Sea. A strong signal needed to be sent that this would not be okay."
The question now is whether the sterner tone is confined to the territorial issue.
"I don't think you can divorce the strong signal given on the South China Sea from the broader relationship," said Mr Bower.
"I think there is a consensus within the administration now that (it needs) to take a more clear tone... so that China does not do things based on false assumptions about where America stands on issues."
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