The State Department voiced "concern" about new legislation enacted by China that authorizes its coast guard to use weapons against foreign ships that Beijing considers to be unlawfully entering its waters.
The text "strongly implies this law can be used to intimidate the PRC's maritime neighbors," State Department spokesman Ned Price said, referring to the People's Republic of China.
"We remind the PRC and all whose forces operate in the South China Sea that responsible maritime forces act with professionalism and restraint in the exercise of their authorities," Price told reporters.
"We are further concerned that China may invoke this new law to assert its unlawful maritime claims in the South China Sea."
Price said that President Joe Biden's administration was reaffirming a statement on the South China Sea issued in July by then secretary of state Mike Pompeo, known for his hawkish stance against Beijing.
In the statement, Pompeo declared that Beijing's claims to offshore resources across most of the South China Sea were "completely unlawful."
The United States has long rejected China's sweeping claims in the strategic waterway but Pompeo went further by explicitly backing the positions of Southeast Asian nations such as the Philippines and Vietnam rather than staying out of the disputes.
Vietnam calls the South China Sea the East Sea.