China urged the United States to "speak and act cautiously" regarding the Taiwan question and the South China Sea issue, a defense spokesperson said on Thursday.

Zhang Xiaogang, the spokesman for the Ministry of National Defense, made these remarks in response to a series of recent comments and actions by the US in the Taiwan Strait and South China Sea.

Earlier this month, the littoral combat ship USS Gabrielle Giffords illegally entered waters near Ren'ai Reef in China's Nansha Islands in South China Sea without the approval of the Chinese government. The US warship's passage was monitored by the People's Liberation Army's Southern Theater Command.

Last week, a US P-8A anti-submarine patrol aircraft transited the Taiwan Strait and hyped up the passage publicly. The PLA's Eastern Theater Command organized air forces to track and monitor the aircraft's passage.

Subsequently, some US officials claimed that they would continue to operate in so called international waters, including the South China Sea and the Taiwan Strait, based on international law.

Zhang responded by saying that China has been consistently respecting the rights of all countries to navigate and overfly in the South China Sea under international law, while he stressed that China firmly opposes any actions that jeopardize its sovereignty and security "under the pretext of freedom of navigation and overflight".

"China has indisputable sovereignty over the Nansha Islands, including the Ren'ai Reef, and their adjacent waters," he said.

"The unauthorized and illegal entry of the US warship into waters near Ren'ai Reef has seriously undermined China's sovereignty and security, violated international law and the basic norms of international relations, disrupting regional peace and stability," the spokesperson said.

He emphasized that Taiwan is inseparable part of China's territory, and that the US should not attempt to challenge China's firm determination to safeguard its national sovereignty and territorial integrity at any time.

According to the United Nations Convention on the Law of the Sea and China's domestic law, the waters of the Taiwan Strait include China's internal waters, territorial sea, a contiguous zone and an exclusive economic zone, said Zhang, underscoring that "there is no such thing as 'international waters'".

He also added that there is not even the concept of "international waters" in international maritime law.

Zhang said that the US claims that the Taiwan Strait is so called international waters is a pretext for manipulating the Taiwan question and threatening China's sovereignty and security, saying that China firmly opposes this.

"China once again urges the US to speak and act cautiously on the Taiwan question and South China Sea issues, stop provocative actions, take concrete actions to implement the important consensus reached by the leaders of the two countries, and create a favorable atmosphere for the healthy and stable development of bilateral military ties," said the spokesman.