China warned Asian neighbors Thursday to stop searching for oil near the Spratly Islands and vowed to assert its sovereignty over the potentially petroleum-rich territory in the South China Sea that several nations claim. China and the Philippines have swapped diplomatic protests over the islands, with Filipino officials accusing Chinese forces of intruding into Manila-claimed areas six times since February and of firing shots at least once. Beijing denied the allegation Thursday and said it would use violence only when attacked. Vietnam, meanwhile, has accused China of flaring tensions in Vietnamese waters by hindering the operation of a oil and gas exploration boat for the second time in two weeks. The Spratlys, which are believed to be atop vast oil and gas reserves, have long been feared as a potential flash point of armed conflict in Asia. The chain of barren, largely uninhabited islands, reefs and banks are claimed wholly by China, Taiwan and Vietnam and partly by the Philippines, Malaysia and Brunei.