BEIJING (REUTERS) - Countries with territorial claims in the South China Sea that look for help from third parties will find their efforts "futile", China's Foreign Minister Wang Yi warned on Thursday, adding that the path of confrontation would be "doomed".

Beijing's assertion of sovereignty over a vast stretch of the South China Sea has set it directly against Vietnam and the Philippines, while Brunei, Taiwan and Malaysia also lay claim to other parts of the sea, making it Asia's biggest potential military troublespot.

At stake are potentially massive offshore oil reserves. The seas also lie on shipping lanes and fishing grounds.

Mr Wang didn't name any third countries, but the United States is a close ally of Taiwan and the Philippines, and has good or improving relations with the other nations laying claim to all or part of the South China Sea. Japan is also boosting defence ties with The Philippines.

"If certain claimant countries choose confrontation, that path will be doomed," Mr Wang said after a speech at the annual Tsinghua World Peace Forum.

"If such countries try to reinforce their poorly grounded claims through the help of external forces, that will be futile and will eventually prove to be a strategic miscalculation not worth the effort."

The Philippine military said this week it had revived plans to build new air and naval bases at Subic Bay, a former U.S. naval base that American forces could use to counter China's creeping presence in the South China Sea.

Mr Wang's comments came days before the minister is due to attend a meeting of foreign ministers of the Association of Southeast Asian Nations grouping in Brunei from Saturday to Tuesday.

The 10-member Aseann hopes to reach a legally binding Code of Conduct to manage maritime conduct in disputed areas. For now a watered-down "Declaration of Conduct" is in place.

The path to a Code of Conduct will be slow and deliberate, Wang said, adding that the Declaration of Conduct was a commitment made by China and the 10 ASEAN countries and China would continue to abide by it.

"The right way is to fully implement the Declaration, and in this process, move forward with the Code in a gradual way," Mr Wang said.