US President Barack Obama said Washington is concerned China is using its "sheer size and muscle" to push around smaller nations in the South China Sea, just hours after Beijing gave a detailed defence of its creation of artificial islands in the contested waterway.
China's rapid reclamation around seven reefs in the Spratly archipelago of the South China Sea has alarmed other claimants, such as the Philippines and Vietnam, and drawn growing criticism from US government officials and the military.
While the new islands will not overturn US military superiority in the region, workers are building ports and fuel storage depots and possibly two airstrips that experts have said would allow Beijing to project power deep into the maritime heart of Southeast Asia.
"Where we get concerned with China is where it is not necessarily abiding by international norms and rules and is using its sheer size and muscle to force countries into subordinate positions," Obama told a town-hall event in Jamaica on Thursday ahead of a Caribbean summit in Panama.
"We think this can be solved diplomatically, but just because the Philippines or Vietnam are not as large as China doesn't mean that they can just be elbowed aside," he said.
China claims most of the potentially energy rich South China Sea, through which $5 trillion in ship-borne trade passes every year. The Philippines, Vietnam, Malaysia, Brunei and Taiwan also have overlapping claims.
China, which has asked Washington not to take sides in the row, says it is willing to discuss the issue with individual countries directly involved in the dispute.
However, it has refused to participate in an international arbitration case filed by the Philippines in The Hague over the contested waterway.
Chinese Foreign Ministry spokeswoman Hua Chunying earlier sketched out plans for the islands in the Spratlys, saying they would be used for military defence as well as to provide civilian services that would benefit other countries.
While she gave no details on their defensive use, Hua told a news briefing that the reclamation and building work was needed partly because of the risk of typhoons in an area with a lot of shipping that is far from land.
"We are building shelters, aids for navigation, search and rescue as well as marine meteorological forecasting services, fishery services and other administrative services" for China and neighbouring countries, Hua said.