Washington (AFP) -- New satellite imagery shows China has apparently installed "significant" defensive weapons on a series of artificial islands it built in the South China Sea, a US-based think tank said Wednesday.
Beijing has created seven islets in the Spratly Islands in recent years, built up from much smaller land protuberances and reefs.
Although Beijing has said it does not intend to militarize the contested waters of the South China Sea, ongoing satellite imagery has shown the installation of military equipment and longer runways.
The latest images, released by the Asia Maritime Transparency Initiative (AMTI), show a series of hexagonal structures now in place on each of the seven islets.
They appear to be large anti-aircraft guns and close-in weapons systems (CIWS), the AMTI said.
Such systems are designed to take out incoming missiles and enemy aircraft.
"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," said AMTI, part of the Washington-based Center for Strategic and International Studies.
"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."
AMTI director and Southeast Asia expert Greg Poling said watching the Chinese military buildup was like seeing pieces of a jigsaw puzzle come together.
China now has air bases, radar and communications systems, naval facilities and defensive weaponry in place.
"I also would expect we will see antiship cruise missiles," Poling told AFP.
"You are beginning to have these interlocking rings of defense around these islands, (extending) China's ability to project power to the south."
The South China Sea issue has 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.
Beijing's territorial claims, based on controversial historical records, have also pitted it against the United States.
China paused land-reclamation efforts last year and began focusing on "infrastructure development" of the islets, according to a US Defense Department report in May.
The United States insists China's claims have no basis under international law, and the US military has conducted several "freedom of navigation" operations in which ships and planes have passed close to the sites Beijing claims.
Such missions have drawn howls of fury from China, which accuses Washington of provocation and increasing the risk of a military mishap.
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 dismissed.
The new satellite images can be viewed at: http://u.afp.com/4iUE.