US Secretary of State Hillary Clinton will meet her Chinese counterpart in Cambodia on Thursday, keen to avoid souring ties amid a fraught background of rows between Beijing and its neighbours.
The US has made a military and economic "pivot" towards Asia in a strategic bid to counteract China's influence in the region, which is home to huge untapped resources and surging economies.
Discussions between Clinton and Chinese Foreign Minister Yang Jiechi at the ASEAN Regional Forum in Phnom Penh come amid a fresh spat over a string of remote islands claimed by Japan and China.
The sudden flare-up of new tensions, sparked by Chinese patrol boats approaching the islands on Wednesday, threatened to overshadow efforts by Southeast Asian nations to agree on a "code of conduct" for disputed waters.
Japan lodged a formal complaint and summoned the Chinese ambassador, while Beijing asserted they "have always been China's territory since ancient times, over which China has indisputable sovereignty".
Japan refers to the islands in the East China Sea as Senkaku and sees a Japanese family as the owners, while China calls them the Diaoyu.
The ten members of Southeast Asian body ASEAN have been attempting to draft a code of conduct for the South China Sea to avert conflicts and create a mechanism for settling disputes.
At the summit, Clinton is likely to try to balance support for US allies Japan, the Philippines and Vietnam -- all angered by China's recent perceived aggression in contested seas -- with efforts to keep Beijing onside, analysts say.
The resource-rich South China Sea, home to vital shipping lanes, is the subject of overlapping claims by Vietnam, the Philippines, Malaysia and others, but is considered almost entirely Chinese by Beijing.
China said it is prepared to discuss a code to boost trust, but it wants to settle territorial disputes bilaterally -- largely because it can bring its huge economic and military clout to bear in negotiations with small neighbours.
A senior US State Department official travelling with Clinton confirmed she will discuss the Japan incident.
The same official told reporters on Monday that the US is "going to be very clear in our determination to see progress on the (South China Sea) code of conduct."
"The entire prosperity of Asia, which is really at the centre of the global economy, rests on the maintenance of peace and stability. So the stakes could not be higher," the official added, requesting anonymity.
Wary of irking China, Clinton will also discuss several less contentious issues with Yang -- such as joint humanitarian response work.
The Philippines is leading a push for ASEAN to unite to persuade China to accept a code of conduct based on a UN law on maritime boundaries that would delineate the areas belonging to each country.
Asked about the Japan-China spat, Philippine Foreign Minister Albert del Rosario told reporters: "It looks like they're (China) becoming more aggressive every day."
Analysts say the sudden outburst over the East China Sea islands will drive anxious neighbouring countries closer to the United States.
"The Chinese huff and bluff with Japan does not augur well," said Southeast Asia expert Carl Thayer, who runs a consultancy. "China's actions have certainly pushed the Philippines towards Washington," he added.
