During a two-day confab in the Chinese capital, US Secretary of State John Kerry urged China to settle its territorial rows peacefully and based on the "rule of law".
But Beijing's top diplomat Yang Jiechi said the United States should butt out of disputes a long way from its shores, including an international arbitration case brought by the Philippines.
China's stance on the case is "in line with international law", Yang said, insisting that Beijing's position "has not and will not change".
The South China Sea has "been China's territory since ancient times" and China "has every right to uphold its territorial sovereignty and lawful and legitimate maritime entitlements", Yang said.
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China claims nearly all of the strategically vital sea despite competing claims by several Southeast Asian neighbours, and has rapidly built artificial islands suitable for military use.
Washington has responded by sending warships close to Chinese-claimed reefs, angering Beijing.
The sour ending to the annual Strategic and Economic Dialogue came despite efforts by both sides to smooth out differences that divide the world's top two economies.