An aerial photo shows Thitu Island, part of the disputed Spratly group of islands, in the South China Sea on July 20, 2011
Washington (AFP) - China recently deployed two artillery pieces on one of its artificial islands in the South China Sea, an unprecedented move that suggests Beijing is trying to extend its military reach in the contested waters, US officials said Friday.
The heavy weapons, since removed, posed no security threat but their positioning -- within range of territory claimed by Vietnam -- underscored Washington's concerns that China is pursuing a massive island-building project for military purposes, officials said.
The two motorized artillery pieces were spotted on a manmade feature about a month ago in the Spratly Islands region, a defense official, speaking on condition of anonymity, told AFP, citing surveillance imagery.
It is the first time that China has been accused of deploying artillery or other weaponry on their manmade islands in the area.
"We can confirm we have identified some weapons on one of these reclaimed Chinese islands," Pentagon spokesman Colonel Steven Warren told reporters.
"The militarization of these islands is something we're opposed to."
China and the United States have been engaged in an escalating war of words over the South China Sea, where Beijing has rapidly built up reefs over about 2,000 acres (800 hectares) -- including 1,500 acres just since January.
The construction includes outposts that could be used for surveillance systems, harbors, an airfield and logistics support, according to a recent Pentagon report on China's military.
On Wednesday, US Defense Secretary Ashton Carter, who is on a 10-day tour of Asia, said Washington wanted "a peaceful resolution of all disputes and an immediate and lasting halt to land reclamation by any claimant."
- Beijing 'out of step' -
The United States has insisted the areas claimed by China are international waters and airspace, and has sent out surveillance planes and naval ships to drive home the point.
The Pentagon chief, speaking in Hawaii, also said "there should be no mistake: The United States will fly, sail, and operate wherever international law allows, as we do all around the world."
Beijing's actions in the South China Sea are "out of step with both international norms" and the "regional consensus" that opposes coercive methods to resolve territorial disputes, Carter said.
China's actions were bringing neighboring countries closer and prompting "increasing demand for American engagement" in the region, he added.
Last week the Chinese military ordered a US Navy P-8 Poseidon surveillance aircraft to leave an area above the heavily disputed Spratly Islands. But the American plane ignored the demand and stated it was flying in what US officials deem to be international airspace.
Beijing has defended its dredging work in the contested waters and accused Washington of singling out China over an activity that other countries in the region are also engaged in.
China insists it has sovereignty over nearly all of the South China Sea, a major global shipping route which is believed to be home to a wealth of oil and gas reserves.
The Philippines, Vietnam, Malaysia, Taiwan and Brunei also claim parts of the sea.
Tensions in the South China Sea will likely dominate the Shangri-La Dialogue this week in Singapore, a major annual security conference that gathers defense ministers and top brass from across Asia. Carter is due to deliver a speech at the conference.