Resolving disputes over the South China Sea is "pivotal" to regional stability, US Secretary of State Hillary Clinton said at security talks on Friday.

Her comments came as China increasingly asserts its power in the region, causing concern to nearby countries as well as the United States.

US commanders have made it clear they are watching China's military buildup, particularly its naval reach into the South China Sea.

Beijing's claims over potentially resource-rich archipelagos in the South China Sea conflict with those of some members of the Association of Southeast Asian Nations (ASEAN).

ASEAN favours a united front on the South China Sea issue but Beijing prefers to deal with the matter bilaterally with individual claimants, and was not happy that Clinton and 11 other delegates raised the matter in Friday's talks, diplomats said.

In Vietnam, which hosted the 27-member ASEAN Regional Forum (ARF) security dialogue, the maritime sovereignty dispute evokes strong public emotions.

Hanoi periodically reports cases of Vietnamese fishing boats and equipment being seized by Chinese vessels.

"The United States has a national interest in freedom of navigation, open access to Asia's maritime commons, and respect for international law in the South China Sea," Clinton said in remarks prepared for the ARF, Asia's largest security dialogue.

"We oppose the use or threat of force by any claimant," she said.

At a security meeting in Singapore last June, US Defence Secretary Robert Gates said Washington objected to any effort to "intimidate" US energy firms in the region.

In a veiled warning to China, Gates alluded to Beijing's alleged threats against some US oil and gas companies interested in off-shore exploration in waters claimed by Vietnam.

ASEAN hopes to ultimately agree with China a binding "regional code of conduct" that will govern actions in the South China Sea and replace a non-binding "declaration" by the claimants not to take destabilising actions in the area.

"We encourage the parties to reach agreement on a full Code of Conduct," Clinton said.

In January, Beijing froze bilateral military ties with Washington over US weapons sales to Taiwan.

earlier related report
China blames desulphurising chemical for oil pipeline blast
Beijing (AFP) July 23, 2010 - Chinese authorities on Friday blamed a chemical used to remove sulphur from crude oil for a blast at a storage facility that caused a spill on the country's northeast coast.

An investigation has found that a desulphurising chemical was mistakenly pumped into pipelines after a tanker had stopped unloading crude at the port city of Dalian last Friday, triggering the explosion, the State Administration of Work Safety said.

About 1,500 tonnes of oil were spilled into the Yellow Sea off Liaoning province, officials said previously.

The government has mobilised hundreds of fishing boats and other vessels to clean up the spill, which an official estimate Monday said affected 435 square kilometres (around 170 square miles) of the Yellow Sea.

However, Chinese media reports later said the slick had spread to 946 square kilometres, and stretched as far as 90 kilometres along the coast.

The government has said about 40 special oil-skimming vessels were leading clean-up efforts and that 23 tonnes of oil-eating bacteria were being employed.

China National Petroleum Corp, the country's biggest oil company and owner of the pipelines that exploded, said in a statement on its website Thursday that at least 400 tonnes of the spilt oil had been cleaned up already.