WASHINGTON (REUTERS) - The new US administration of President Donald Trump vowed on Monday that the United States would prevent China from taking over territory in international waters in the South China Sea, something Chinese state media has said would require Washington to "wage war".

"I think the US is going to make sure that we protect our interests there," White House spokesman Sean Spicer told a news briefing. "It's a question of if those islands are in fact in international waters and not part of China proper, then yeah, we're going to make sure that we defend international territories from being taken over by one country."

Mr Spicer was responding to a question as to whether Mr Trump agreed with comments by his Secretary of State nominee Rex Tillerson on Jan 11 that China should not be allowed access to islands it has built in the contested South China Sea.

Mr Tillerson's remarks at his Senate confirmation hearing prompted Chinese state media to say the US 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.

Mr Tillerson said at the hearing, when asked whether he supported a more aggressive posture towards China: "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 chairman and chief executive did not elaborate on what might be done to deny China access to the islands.

China's Foreign Ministry said it could not guess what Mr Tillerson meant by his remarks, which came after Mr Trump questioned Washington's longstanding and highly sensitive "one China" policy over Taiwan.

Aides have said that Mr Trump, who took office on Friday, plans a major naval build-up in East Asia to counter China's rise.