Washington has declared that it will push Beijing on the issue of disputed islands, promising to "test" China while accusing the emerging Asian superpower of abusing its "might."
President Barack Obama, in an interview with Channel News Asia, said his administration will "continue to test" Beijing's pledge to not militarize the disputed South China Sea.
He accused China of abusing its power in the region by placing missiles on islands in the disputed Parcel archipelago.
"We think China is resorting to the old style of might makes right, as opposed to working through international law and international norms to establish claims, and to resolve disputes," Obama said. The US President made the comments following a summit of Southeast Asian nations and after reports that included satellite imagery purporting to show missile systems being set up on the islands.
China and other nations - including Vietnam and Taiwan - all claim islands in the region but China has argued that the chain belongs exclusively to them.
The Philippine government has earlier said China's action was considered a "clear violation" of the Declaration on the conduct of parties in the South China or DoC and other relevant Asean-China Declarations and Statements.
The DoC is a nonbinding political accord signed in 2002 by China and Asean members Philippines, Malaysia, Vietnam, Brunei, Singapore, Thailand, Indonesia, Cambodia, Laos and Myanmar.
It discourages aggressive actions and bars construction of new structures in the contested region that could spark armed conflicts.
But many regard the 2002 accord as lacking in teeth and a dispute-settlement scheme to effectively deal with the territorial disputes, sparking calls for a more effective and legally-binding Code of Conduct.
China, Manila said, "put into question the good faith of China" to work with Asean for the early conclusion of a code of conduct, and "to cooperate in the efforts of all parties to find ways forward on the peaceful settlement of disputes in accordance with UNCLoS."
Manila has a pending case against China before the The Hague-based Permanent Court of Arbitration. A final decision, Philippine diplomats said, may be handed down in May.
The Chinese Defense Ministry, meanwhile, called reports about the missile deployment "hype by certain Western media outlets," adding it has controlled the Paracels since the end of the Vietnam War.