June 5 (UPI) -- China warned the United States and Japan against "intervening" in its buildup in the South China Sea after U.S. Defense Secretary James Mattis criticized China's land reclamation activities in the disputed Spratly Islands.
Beijing's foreign ministry spokeswoman Hua Chunying told reporters Monday that China has "taken note of the irresponsible remarks of U.S. and Japanese officials," South Korean news agency Yonhap reported.
"China strongly protests the statement and opposes the declaration," Hua said. "Some countries harbor ulterior motives, which is why they make false statements and preach in black-and-white concepts."
Mattis said at the Shangri-La Dialogue in Singapore he was opposed to China's militarization of reclaimed islands in the South China Sea.
The activities "undermine regional stability," demonstrate "China's disregard for international law" and its "contempt for other nations' interests," Mattis had said, according to Japan's Yomiuri Shimbun.
The U.S. defense secretary added the Pentagon plans to continue freedom-of-navigation operations in the maritime region.
Hua disagreed that Beijing's buildup challenged stability.
"China holds sovereignty over the Spratly Islands of the South China Sea," the spokeswoman said. "China respects freedom of navigation and flight of each country in the South China Sea, but some countries are using force to threaten China's sovereignty and security."
Japanese Defense Minister Tomomi Inada also condemned China's maritime construction and said Chinese ships trespass into Japan-claimed waters.
"In the East China Sea, government ships of a certain country continue to make periodic incursions into Japanese territorial waters," Inada said.
Hua said China's patrol of waters near the disputed Senkaku Islands is "legal" because they "have been China's territory since ancient times."
"We will continue patrol activities," Hua said. "Japan's claims do not match the truth, we urge Japan to make constructive efforts."