China's bold claim in tense dispute :'OUR TERRITORY'

China has made one of its strongest claims yet to territory in the highly-disputed South China Sea, with its comments undoubtedly set to enrage its Southeast Asian neighbours.

Beijing says it has the right to develop South China Sea islands as it sees fit in the wake of US accusations that it has fully militarised at least three of several islands it built in violation of a previous commitment.

China's deployment of "necessary national defence facilities on its own territory is a right entitled to every sovereign country and is in line with international law, which is beyond reproach," Foreign Ministry spokesperson Wang Wenbin told reporters at a daily briefing on Tuesday.

US military activities in the area aimed to "stir up trouble and make provocations," Mr Wang said.

"That seriously threatens the sovereignty and security of coastal countries and undermines the order and navigation safety in the South China Sea."

Australia has previously expressed its concerns over China's military development in the region, with Defence Minister Peter Dutton repeatedly warning of the increased chance of military conflict.

Largest post-war military build up, US says

On Sunday, US Indo-Pacific Commander Admiral John C. Aquilino said China had armed the islands with anti-ship and anti-aircraft missile systems, laser and jamming equipment, and fighter jets, in an increasingly aggressive move that threatens all nations operating nearby.

Aquilino said the hostile actions were in stark contrast to Chinese President Xi Jinping's past assurances that Beijing would not transform the artificial islands in contested waters into military bases. The efforts were part of China's flexing of its military muscle, he said.

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"I think over the past 20 years we've witnessed the largest military buildup since World War II by the PRC," Aquilino told The Associated Press in an interview, using the initials of China's formal name.

"They have advanced all their capabilities and that buildup of weaponisation is destabilising to the region."

China claims as its own territory virtually the entire South China Sea, home to fish stocks and undersea minerals, along with sea lanes through which an estimated $US5 trillion in global trade travels each year.

China refuses to acknowledge claims from five other governments to some or all of the waterway and dismissed the findings of a UN-backed arbitration tribunal that invalidated China's sweeping historical claims under the UN Convention on the Law of the Sea.

The fully militarised islands are among seven China has constructed in recent years by piling sand and concrete atop coral reefs, causing heavy damage to the marine environment.

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