President Barack Obama said on Thursday the United States is concerned China uses its "sheer size and muscle" to push around smaller countries in the South China Sea.
His comments come after China defended its construction of artificial islands in the South China Sea, saying it is needed to safeguard its sovereignty in the mineral-rich waters where China's territorial claims overlap those of Vietnam, the Philippines, Malaysia, Brunei and Taiwan.
"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 town-hall event in Jamaica ahead of a Caribbean summit in Panama, where he hopes to reassert U.S. leadership in Latin America.
"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."
Chinese officials said the reclamation work would be used for military defences and to provide services that would benefit other countries. The U.S. State Department said the activity was causing anxiety in the region about China's intentions.
China's sovereignty claims over the stretch of water off its south coast and to the east of mainland Southeast Asia set it directly against U.S. allies Vietnam and the Philippines, while Brunei, Taiwan and Malaysia also have claims.
At stake is control over what are believed to be significant reserves of oil and gas.
Obama, speaking to young people in Jamaica, also said the United States encourages Chinese investments around the world, but the deals need to benefit the people of those countries.
(Additional reporting by Matt Spetalnick. Editing by Jason Szep and Andre Grenon)