Story highlights The South China Sea has belonged to China since ancient times, President Xi Jinping says

The United States and allies in the region criticize China's territorial claims

Last month, a U.S. warship made a close pass by a reef China claims

(CNN) The South China Sea is Chinese territory, Chinese President Xi Jinping said in a speech in Singapore Saturday, according to Chinese state-run media.

Xi added that his nation would settle disputes over contested waters with other powers in the region,

China has recently built artificial islands in the sea on top of previously submerged reefs, and has met with harsh criticism from the United States and key allies in the region, who accuse China of trying to expand its maritime territorial claims.

Late last month, a U.S. Navy warship made a close pass by built-upon reefs that China claims as its territory in contested waters . Chinese ships and aircraft tracked the U.S. ship, and China's foreign ministry summoned the U.S. ambassador to the country to complain bitterly about the pass.

In his speech at the National University of Singapore on Saturday, Xi disputed that free passage has been a problem.

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