US Secretary of State Hillary Clinton and her Chinese counterpart Yang Jiechi pledged Thursday to work more closely together after talks designed to smooth their countries' often spiky relations. After a meeting in Cambodia, Clinton highlighted areas of common interest such as disaster relief and disease control, which she said were "an important signal that the US and China not only can, but will work together in Asia".

Yang said: "China and US relations have continued to make progress this year," adding both sides had agreed to "enhance our dialogue... to continue to expand our common ground".

There have been concerns that the US's new foreign policy "pivot" to focus on Asia, where it hopes to counter China's enormous clout, could antagonise Beijing ahead of a leadership transition later this year.

The display of togetherness on the sidelines of a regional Asian security meeting came despite constant friction in the world's most significant bilateral relationship, caused by China's economic and military rise.

Clinton had been expected in Cambodia in conciliatory mood, in contrast to the ASEAN Regional Forum of 2010 when she angered Beijing by saying the US had a "national interest" in the disputed South China Sea.

Tensions over the sea flared again on Thursday when the Philippines accused Beijing of "duplicity, intimidation and the threat of the use of force" to stake its claim to a rocky outcrop claimed by Manila in the resource-rich sea.

On Wednesday, Japan lodged a formal complaint with China after three Chinese boats approached islands controlled by Japan in the East China Sea. Vietnam has also recently accused Beijing of aggression in contested seas.

Clinton deliberately steered clear of being drawn into the spats or pointing the finger at China, which claims almost all of the sea, but she expressed alarm about the potential for territorial disputes to escalate.

"No nation can fail to be concerned by the increase in tensions, the uptick in confrontational rhetoric and disagreements over resource exploitation," Clinton told a press conference.

Clinton has urged progress on a long-stalled code of conduct for the South China Sea to avoid "confusion and even confrontation" over shipping and fishing rights in the waterway, which is home to key shipping lanes.

There were little signs of movement, however, with Southeast Asian nations in regional bloc ASEAN deeply divided over what should be included and China apparently in no mood to begin discussions, diplomats said.

China said on Wednesday it would only begin negotiating the code with ASEAN "when conditions are ripe".

"The qualifying statement -- when the time is ripe -- means that planned talks in September (to advance on formulating a code) are unlikely to take place," one Asian diplomat told AFP on condition of anonymity.

The Philippines is leading a push for ASEAN to unite to propose a code of conduct based on a UN law on maritime boundaries that would delineate the areas of the sea belonging to each country.

Other countries, led by staunch China ally Cambodia, are pushing back in a bid to avoid antagonising Beijing, which wants all territorial disputes to be settled bilaterally and rejects "internationalising" the issue.

Such is the discord within the 10-member ASEAN grouping over their approach to China that foreign ministers have been unable to agree on a joint statement, diplomats say.

Analysts say Clinton has been trying to balance support for US allies Japan, the Philippines and Vietnam -- all angered by China's apparent aggression in contested seas -- with efforts to keep Beijing onside.

The unexpected row between Japan and China in the East China Sea on Wednesday is also seen as likely to heighten the anxiety of China's neighbours and drive them further into the United States' orbit.

"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."