Washington is hoping China will accept a code of conduct for resolving territorial disputes in the resource-rich South China Sea, a difficult mediation effort that has often been rebuffed by the communist government.
Hillary Clinton, the US secretary of state, is meeting on Thursday with China's foreign minister on the sidelines of a Southeast Asian conference.
Governments in the region are increasingly worried about Beijing's expansive maritime claims, and Chinese tensions with the Philippines and Vietnam have threatened to boil over.
Speaking to foreign ministers gathered in Cambodia, Clinton said the US is not taking sides. She added that Washington wants to ensure freedom of navigation and peace.
China and the US are closely entwined economically and increasingly on the diplomatic front, but they have clashed repeatedly over issues ranging from Tibet and Taiwan to trade and the value of the Chinese currency.
The 10 members of Southeast Asian regional body ASEAN have been trying to agree a long-stalled "code of conduct" for the disputed South China Sea, home to vital shipping lanes, to help settle overlapping claims.
The Philippines is leading a push for ASEAN to unite and draw up a code based on a UN law on maritime boundaries that would delineate the areas belonging to each country. Beijing is unlikely to accept this, however.
This push came as Beijing invited bids for exploration of oil blocks in waters claimed by Vietnam, which sparked protests on the streets of Hanoi.
China's assertiveness in the resource-rich South China Sea is seen by analysts as pushing anxious neighbouring countries closer to the United States.
China blasts Clinton
China's top newspaper slammed Clinton on Thursday for comments she made lauding democracy and implicitly criticising restrictions in China, saying those Asian countries that ape US democracy were doomed to fail.
In China's first response to her remarks, ruling Communist Party mouthpiece The People's Daily said Clinton was acting as a "preacher for human rights" by praising certain countries to obliquely attack China.
The newspaper added that Asian countries were now booming, unlike Western countries stuck in the morass of economic crisis, proving they could go down "a path different from the West and create political systems which suit their national characteristics".
Earlier this week, Clinton held up Mongolia's sometimes messy politics as a democratic model for Asia. While she did not directly name China, her comments appeared aimed partly at Beijing.
The sea hosts about a third of the world's cargo traffic, has rich fishing grounds and is believed to store vast oil and gas reserves.