WASHINGTON (Reuters) - China appears to have installed weapons, including anti-aircraft and anti-missile systems, on all seven of the artificial islands it has built in the South China Sea, a U.S. think tank reported, citing new satellite imagery.

A satellite image shows what CSIS Asia Maritime Transparency Initiative says appears to be anti-aircraft guns and what are likely to be close-in weapons systems (CIWS) on the artificial island Subi Reef in the South China Sea in this image released on December 13, 2016. Courtesy CSIS Asia Maritime Transparency Initiative/DigitalGlobe/Handout via REUTERS

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

China said on Thursday that, while its construction on islands and reefs in the South China Sea was mainly for civilian use, it was “legitimate and normal” for it to take steps to defend its territory.

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-defense fortifications already constructed at China’s smaller facilities on Gaven, Hughes, Johnson, and Cuarteron reefs,” it said citing images taken in November.

“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 defense 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 defense against cruise missiles launched by the United States or others against these soon-to-be-operational air bases.”

Chinese Foreign Ministry spokesman Geng Shuang told a regular news briefing in Beijing that he “did not understand” the situation referred to in the report.

“The Nansha islands are China’s inherent territory. China’s building of facilities and necessary territorial defensive facilities on its own territory is completely normal,” he said, using China’s name for the Spratlys.

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“If China’s building of normal facilities and deploying necessary territorial defensive facilities on its own islands is considered militarization, then what is the sailing of fleets into the South China Sea?” he added, in an apparent reference to U.S. “freedom of navigation” patrols in the waters.

PHILIPPINES SAYS “BIG CONCERN”

The Philippines, one of several countries with competing territorial claims in the South China Sea, said it was still verifying the report.

“But if true it is a big concern for us and the international community who use the South China Sea lanes for trade,” said Defense Minister Delfin Lorenza during a visit to Singapore with President Rodrigo Duterte.

“It would mean that the Chinese are militarizing the area which is not good.”

Vietnam’s foreign ministry did not immediately respond to requests for comment.

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 militarization. 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 militarizing, 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.

“READY YOUR SLINGSHOT”

Singapore-based South China Sea expert Ian Storey said he believed the move would help ready the facilities for the probable next step of China flying jet fighters and military transport planes to its new runways.

“From the outset it’s been quite obvious that the artificial islands were designed to serve as military outposts in the South China Sea,” said Storey, of the ISEAS Yusof Ishak Institute.

“Even while tensions are at a relatively low ebb, I think we can expect to see military flights to the Spratlys in the coming months – including the first jet fighters,” Storey said.

The United States has criticized what it called China’s militarization of its maritime outposts and stressed the need for freedom of navigation by conducting periodic air and naval patrols near them that have angered Beijing.

U.S. President-elect Donald Trump, who takes office on Jan. 20, has also criticized Chinese behavior in the South China Sea while signaling he may adopt a tougher approach to China’s assertive behavior in the region than President Barack 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 militarization of disputed features.”

China’s Defense Ministry said in a statement on its microblog on Thursday that it was “legitimate and lawful” for it to place defensive military installations on islands where it said Beijing had “indisputable sovereignty”.

“If someone makes a show of force at your front door, would you not ready your slingshot?” it said.