The United States says five Chinese ships shadowed and maneuvered dangerously close to a US Navy vessel in what appeared to be an effort to harass the American crew.
The Obama administration is protesting to the Chinese government. The protest will be delivered to Beijing's military attache on Monday.
The Defense Department said in a statement that a Chinese intelligence ship and several others surrounded the USNS Impeccable, an unarmed vessel with a civilian merchant marine crew. The U.S. vessel was conducting ocean surveys Sunday in international waters in the South China Sea.
"The unprofessional manoeuvres by Chinese vessels violated the requirement under international law to operate with due regard for the rights and safety of other lawful users of the ocean," said Pentagon spokesman Marine Maj Stewart Upton.
"We expect Chinese ships to act responsibly and refrain from provocative activities that could lead to miscalculation or a collision at sea," he said.
The statement said the Navy sprayed one ship with water from fire hoses to force it away and the Chinese crew members stripped to their underwear and continued closing within 25 feet.