China urged the United States Navy to cease provocative and risky actions in the South China Sea, and promised to take every measure necessary to safeguard national sovereignty and security.

The USS Gabrielle Giffords littoral combat ship sailed within 12 nautical miles of Meiji Reef near the Nansha Islands on Wednesday, and the USS Wayne E. Meyer guided-missile destroyer sailed into territorial waters of the Xisha Islands on Thursday, the US Navy said.

These maneuvers were all conducted without permission from China, Geng Shuang, Foreign Ministry spokesman said on Friday. "The US' actions have seriously undermined China's sovereignty and security interests and damaged peace and stability in the South China Sea. China strongly opposes such actions and has lodged stern representations with the US," Geng said.

The Southern Theater Command of the People's Liberation Army mobilized air and maritime forces to identify and warn the US ships to leave in accordance with laws and regulations, Senior Colonel Li Huamin, spokesman of the theater command, said in an online statement on Friday.

Geng said that China has always respected and upheld each nations' right of passage and flight in the South China Sea so long as it abides by international laws. "But we absolutely oppose any country using freedom of navigation and flight as an excuse to undermine China's sovereignty and security," he said.

The situation in the region is generally stable, and various parties involved are focused on dialogue and collaboration. "We urge the US side to immediately stop such provocative actions, and not act against the trend of the times to avoid damaging the region's peace and stability," Geng added.

"China will take all measures necessary to adamantly safeguard national sovereignty and peace, and maintain peace and stability in the South China Sea," he said.

Li said the US military has frequently sent planes and warships to the South China Sea to stir up trouble under the pretense of freedom of navigation. "We urge the US side to stop such provocative and risky actions to avoid any unforeseeable accidents," he said.

China has undisputable sovereignty over the islands and its surrounding waters in the South China Sea. "No matter what trickery the US pulls from its hat, the Chinese military has the resolution and capability to protect its national sovereignty and security, as well as maintain peace and stability in the region," he said.

In a speech in Vietnam on Wednesday, US Secretary of Defense Mark Esper accused China of using "coercion and intimidation" against smaller Asian nations in the South China Sea and urged them to push back. He also said the US will provide Vietnam's coast guard with a ship next year, though no details were given, according to US media reports.

On Monday, during a meeting between Esper and State Councilor and Minister of National Defense General Wei Fenghe in Thailand, Wei asked the US to "stop flexing muscles in the South China Sea and not provoke and escalate tensions in the region", said ministry spokesman Senior Colonel Wu Qian.