China has strategically positioned weaponry in one of the artificial islands it built in the highly contested waters of the South China Sea, further increasing the demand for US intervention by Southeast Asian countries with competing claims, sources said.

Although Chinese artillery pieces are no longer visible after being removed or hidden after a US Navy P8-A Poseidon surveillance mission over the area spotted such weaponry, US Defence Secretary Ashton Carter maintained that the United States will not stop its military operations around Chinese-claimed islands in disputed waters 600 miles from China's coastline, CNN reported on Thursday.

"There should be no mistake: The United States will fly, sail and operate wherever international law allows, as we do all around the world," Carter said on Wednesday.

China earlier asked the US to stop what Chinese Foreign Ministry spokesperson Hua Chunying described as "provocative speech and acts."

"China urges the US, think three times before taking action; act responsibly; stop all provocative speech and acts; and do more things that will benefit the region's peace and stability instead of the opposite," Hua said.

"What kind of function can the US have for the region's peace and prosperity?" the foreign ministry spokesman asked. "Fundamentally speaking, would creating a mess in the Asia Pacific, which is the core engine of the world economy, fit the US interests?"

During the P8's mission, Chinese Navy repeatedly warned the US crew, who answered each radio challenge with the same response that the US was flying in international airspace over international waters.

"China's actions are bringing countries in the region together in new ways," Carter said. "And they're increasing demand for American engagement in the Asia-Pacific. We're going to meet it. We will remain the principal security power in the Asia-Pacific for decades to come."

Earlier this week, China has warned against an "inevitable" US-China war if the US does not back down from taking part in territorial issues concerning the South China Sea, ValueWalk reported.

"If the United States' bottom line is that China has to halt its activities, then a US-China war is inevitable in the South China Sea," according to the State Council's white paper as reported on Tuesday.

China maintains that it does not want a war, according to Communist Party mouthpiece Global Times, but said any more interference by "external countries" could set off war and Beijing will "accept" it.

The People's Liberation Army (PLA) said it is set to focus more on boosting its efforts to building offensive capabilities.

The military said it is ready to use force beyond its borders in the air and at sea "to safeguard its maritime possessions."