"[United States] and ASEAN leaders agreed on a series of principles for maritime security yesterday," Rhodes said when asked on Twitter how Washington and ASEAN leaders would respond to Beijing’s surface-to-air missiles deployment.
Rhodes noted that efforts to militarize the South China Sea "should be opposed by all who support peace, security and development in the region."
The United States, he added, "will support freedom of navigation and maritime capabilities/efforts to resolve claims under intl [international] law."
Earlier on Tuesday, US media reported citing Taiwanese and US officials that China had deployed two batteries of eight surface-to-air missile and radar systems on Woody Island in the South China Sea.
China and a number of other countries, including Vietnam, Taiwan and Malaysia, have rival claims to hundreds of islands and reefs in the South China Sea.
Beijing has claimed sovereignty over the Spratly Islands and a 12-nautical-mile zone that surrounds them, but Washington has persistently challenged its claims by conducting patrols near the islands citing freedom of navigation.