BEIJING (REUTERS, AFP) - China said Thursday (Dec 15) that the deployment of weapons in the South China Sea had "nothing to do with militarisation", calling the construction of defensive facilities "normal".

Speaking at a regular press briefing, foreign ministry spokesman Geng Shuang told journalists that he was not aware of the report, but said that islands in the South China Sea were the country's "inherent territory".

"To conduct construction on China's own territory and deploy necessary national defence facilities is quite normal," he said, adding that the deployment of defensive weapons had "nothing to do with militarisation".

The comments came after a US think tank reported on Wednesday that China appeared to have installed weapons, including anti-aircraft and anti-missile systems, on all seven of the artificial islands it has built in the busy waterway, citing new satellite imagery.

The Asia Maritime Transparency Initiative (AMTI) at the Centre for Strategic and International Studies said its findings come despite statements by the Chinese leadership that Beijing has no intention to militarise the islands in the strategic trade route, where territory is claimed by several countries.

AMTI said it had been tracking construction of hexagonal structures on Fiery Cross, Mischief and Subi reefs in the Spratly Islands since June and July. China has already built military length airstrips on these islands.

"It now seems that these structures are an evolution of point-defence fortifications already constructed at China's smaller facilities on Gaven, Hughes, Johnson, and Cuarteron reefs," it said citing images taken in November and made available to Reuters. "This model has gone through another evolution at (the) much-larger bases on Fiery Cross, Subi and Mischief reefs."

Satellite images of Hughes and Gaven reefs showed what appeared to be anti-aircraft guns and what were likely to be close-in weapons systems (CIWS) to protect against cruise missile strikes, it said.

Images from Fiery Cross Reef showed towers that likely contained targeting radar, it said.

AMTI said covers had been installed on the towers at Fiery Cross, but the size of platforms on these and the covers suggested they concealed defence systems similar to those at the smaller reefs.

"These gun and probable CIWS emplacements show that Beijing is serious about defense of its artificial islands in case of an armed contingency in the South China Sea," it said. "Among other things, they would be the last line of defence against cruise missiles launched by the United States or others against these soon-to-be-operational air bases."

AMTI director Greg Poling said AMTI had spent months trying to figure out what the purposes of the structures was.

"This is the first time that we're confident in saying they are anti-aircraft and CIWS emplacements. We did not know that they had systems this big and this advanced there," he told Reuters. "This is militarisation. The Chinese can argue that it's only for defensive purposes, but if you are building giant anti-aircraft gun and CIWS emplacements, it means that you are prepping for a future conflict.

"They keep saying they are not militarising, but they could deploy fighter jets and surface-to-air missiles tomorrow if they wanted to," he said. "Now they have all the infrastructure in place for these interlocking rings of defense and power projection."

The report said the installations would likely back up a defensive umbrella provided by a future deployment of mobile surface-to-air missile (SAM) platforms like the HQ-9 system deployed to Woody Island in the Paracel Islands, farther to the north in the South China Sea.

It forecast that such a deployment could happen "at any time," noting a recent Fox News report that components for SAM systems have been spotted at the southeastern Chinese port of Jieyang, possibly destined for the South China Sea.

China has said military construction on the islands will be limited to necessary defensive requirements.

Its defence ministry said on a verified social media account that the construction was mostly for civilian use, and that necessary military installations were for self-defence.

"If someone were flexing his muscles outside your door, wouldn't you get a slingshot ready?", it wrote.

Tensions in the strategic area have been brewing for years, with China, the Philippines, Brunei, Malaysia and Vietnam making competing claims in waters with vital global shipping routes and what is believed to be significant oil and natural gas deposits.

The Philippine foreign ministry said Manila was still independently verifying the AMTI report. If true, "then it is a cause for serious concern because it tends to raise tension and undermine peace and stability in the region," spokesman Charles Jose told AFP.

In a statement sent to AFP, Australia's foreign minister Julie Bishop said that the building of artificial islands and possible militarisation was "creating an environment of tension and mistrust" in the region.

Without naming China, she said Australia urged countries to "refrain from coercive behaviour and unilateral actions designed to change the status quo in disputed areas" and warned such behaviour would lead to "reputation and other costs".

Beijing's territorial claims, based in part on controversial historical records, have also pitted it against the United States. The American military has conducted several "freedom of navigation" operations in which ships and planes have passed close to the sites Beijing claims.

The US has sailed warships near the islands, but the ships have not passed within the 12 nautical mile zone that international law defines as territorial waters. Such missions have drawn protests from China, which accuses Washington of provocation and increasing the risk of a military mishap.

At a meeting with Barack Obama in 2015 China's president Xi Jinping pledged Beijing "does not intend to pursue militarisation" in the South China Sea.

The Permanent Court of Arbitration in The Hague ruled in July that there was no legal basis to China's claims to nearly all of the South China Sea, a verdict Beijing has dismissed.

US President-elect Donald Trump, who takes office on Jan 20, has also criticised Chinese behavior in the South China Sea while signaling he may adopt a tougher approach to China's assertive behaviour in the region than President Obama.

The State Department said it would not comment on intelligence matters, but spokesman John Kirby added: "We consistently call on China as well as other claimants to commit to peacefully managing and resolving disputes, to refrain from further land reclamation and construction of new facilities and the militarisation of disputed features."