China has reassured the US it has no intention of withholding "rare earth" minerals from the market, the US Secretary of State has said.
China suspended export of the metals, key to some high-tech industries, to Japan after a diplomatic spat.
The US has pressed China, which has pledged not to use the minerals as a diplomatic weapon, to defuse the row.
Representatives from China and Japan also held informal talks on the fringes of an Asean conference in Vietnam.
US officials said Hillary Clinton's Chinese counterpart, Yang Jiechi, told the US secretary of state that his country would not use rare earths as a diplomatic, political or economic tool in dealing with other countries.
Cooling the row
After the meeting, Hillary Clinton said: "Foreign Minister Yang clarified that China has no intention of withholding these minerals" from the world market, according to AFP.
China also said it did not want their export to become an issue in its foreign relations.
The US has encouraged China to cool the row with Japan and, according to Reuters, has offered to host a trilateral meeting with China and Japan to resolve the dispute between the two.
China produces some 97% of these valuable commodities, which are used to produce electronic items such as mobile phones and equipment for the car industry.
During the 1990s and for much of the past decade, China was able to produce rare earths more cheaply than other countries, leading to the closure of mines elsewhere, notably in Australia and the US.
But Mrs Clinton has said the recent Chinese export restrictions are a "wake-up call" for the world to seek additional sources of rare earths.
The stoppage followed a spat between China and Japan last month over islands whose ownership is disputed.
The islands - known in Japan as Senkaku and in China as Diaoyu - are controlled by Japan, but claimed by China. They are close to key shipping lanes, offer rich fishing grounds and are thought to contain oil deposits.