China risks further alienating regional neighbours and building a "Great Wall of self-isolation" as it pursues its military expansion across the South China Sea, US defence secretary Ashton Carter warned on Saturday.
Speaking at a security summit in Singapore, Carter said countries across the Asia-Pacific region continue to fret over China's sweeping claims of sovereignty in the South China Sea, and its attempts to bolster these by creating military bases on reclaimed islets and increasing maritime patrols.
"China's actions in the South China Sea are isolating it, at a time when the entire region is coming together and networking," Carter said in a speech at an annual forum known as the Shangri-La Dialogue.
"Unfortunately, if these actions continue, China could end up erecting a Great Wall of self-isolation."
Beijing's claim to nearly the entire South China Sea has angered Southeast Asian neighbours and pitted it against the United States, which has conducted patrols near Chinese-held islands to press for freedom of navigation. The contested waters encompass key global shipping lanes.
The Philippines, Brunei, Malaysia and Vietnam have competing claims in the area, which is believed to have significant oil and gas deposits.
The Philippines has filed a case against China before the Permanent Court of Arbitration in The Hague and a decision is expected in the coming weeks but China has said it will not recognise any ruling.
"The United States views the upcoming ruling ... as an opportunity for China and the rest of the region to recommit to a principled future, to renewed diplomacy, and to lowering tensions, rather than raising them," Carter said.
The key to regional security, Carter said, was enhanced military cooperation across the region and the observance of "core principles" such as the peaceful resolution of disputes through legal means and the development of a "principled security network."
"Only when everyone plays by the same rules can we avoid the mistakes of the past, like when countries challenged one another in contests of strength and will, with disastrous consequences for the region," Carter said.
He also suggested the United States and China would benefit from better military ties -- both to build understanding and to avoid the risk of mishaps.
According to the Pentagon, two Chinese fighters last month conducted an "unsafe" intercept of a US spy plane in international air space over the South China Sea, further heightening tensions in the strategically vital waters.
"America wants to expand military-to-military agreements with China to focus not only on risk reduction, but also on practical cooperation," Carter said.
His attendance at the summit is part of a broader US diplomatic push, known as the Asia "rebalance", to build and maintain alliances in the Asia-Pacific region, which America sees as key to its own long-term economic and security interests.
According to a Pentagon report last month, China put its land reclamation efforts on hold in the Spratly Islands chain at the end of 2015. Instead, it focused on adding military infrastructure to its reclaimed features.
In all, China has added more than 3,200 acres (1,295 hectares) of land to the seven features it occupies in the Spratlys, the report found, and it has added lengthy runways to three of these.
The Shangri-La Dialogue is organized by the London-based International Institute for Strategic Studies (IISS).
