BEIJING, May 25 (Xinhua) -- China on Thursday voiced strong protest against a U.S. Navy warship passing close to the Mischief Reef in the South China Sea.

"The USS Dewey illegally entered the waters near the island on early Thursday without permission of the Chinese government," said Chinese Foreign Ministry spokesperson Lu Kang at a press briefing. "Such moves have undermined China's sovereignty and security, and were very likely to cause unexpected air and sea accidents."

The Chinese navy identified the U.S. warship, warned and expelled it, Lu said.

"China has indisputable sovereignty of the Nansha Islands and its adjacent waters. China always respects and maintains the freedom of navigation and overflight of various countries in the South China Sea in accordance with international law," Lu said. "However, we firmly oppose any country damaging China's sovereignty and security in the name of navigation and overflight freedom."

Lu said the situation in the South China Sea has improved and shown positive development momentum, adding that the U.S. acts have severely disrupted negotiations between all parties concerned.

"China is resolute in its determination to maintain sovereignty, security and maritime interests," he said, urging the U.S. side to correct its mistakes, stop provocation and not harm regional peace and stability as well as China-U.S. cooperation.