In a move to increase tension with the U.S., China said Tuesday it had "irrefutable" sovereignty over disputed islands in the South China Sea. Comments by White House spokesman Sean Spicer about China's artificial islands in the Sea, some capable of military use, have upped the ante in the dispute."China has indisputable sovereignty over the South China Sea islands and their adjacent waters," foreign ministry spokeswoman Hua Chunying told a regular press briefing, adding that the country is "firm in safeguarding our rights and interests." "The United States is not a party to the South China Sea issue."Spicer said Monday that the US "is going to make sure we protect our interests" in the Sea when asked if Trump agreed with comments by his secretary of state nominee, Rex Tillerson. On Jan. 11, Tillerson said China should not be allowed access to islands it has built in the contested South China Sea."If those islands are, in fact, in international waters and not part of China proper, yeah, we'll make sure we defend international interests from being taken over by one country," he said.China claims most of the South China Sea, while Taiwan, Malaysia, Vietnam, the Philippines and Brunei claims parts of the sea that commands strategic sealanes and has rich fishing grounds along with oil and gas deposits.China's sovereignty over the Spratly Islands in the South China Sea was "irrefutable" Hua said. But China was also dedicated to protecting freedom of navigation and wants talks with nations directly involved to find a peaceful solution."We urge the United States to respect the facts, speak and act cautiously to avoid harming the peace and stability of the South China Sea," Hua said."Our actions in the South China Sea are reasonable and fair. No matter what changes happen in other countries, what they say or what they want to do, China's resolve to protect its sovereignty and maritime rights in the South China Sea will not change," she added.Tillerson's remarks at his Senate confirmation hearing prompted Chinese state media to say at the time that the United States would need to "wage war" to bar China's access to the islands, where it has built military-length air strips and installed weapons systems.Tillerson was asked at the hearing whether he supported a more aggressive posture toward China and said: "We're going to have to send China a clear signal that, first, the island-building stops and, second, your access to those islands also is not going to be allowed."The former Exxon Mobil Corp (XOM.N) chairman and chief executive did not elaborate on what might be done to deny China access to the islands.But analysts said his comments, like those of Spicer, suggested the possibility of U.S. military action, or even a naval blockade. Such action would risk an armed confrontation with China, an increasingly formidable nuclear-armed military power. It is also the world's second-largest economy and the target of Trump accusations it is stealing American jobs.Spicer declined to elaborate when asked how the United States could enforce such a move against China, except to say: "I think, as we develop further, we'll have more information on it."