China dispatched a converted naval vessel last week to patrol fishing grounds surrounding the disputed Paracel Islands, about 640km south of Hong Kong. China, Taiwan and Vietnam all claim the islands.

Naval argument

The US says its navy survey vessel was in international waters, but China says it was in its exclusive economic zone.

During the incident which took place on March 7, the Impeccable was allegedly surrounded by Chinese boats.

US officials filed a formal diplomatic protest accusing the Chinese of acting in a provocative and dangerous manner.

China insisted the Impeccable was carrying out sensitive activities without Beijing's permission and that its ships were merely enforcing Chinese law.

The Pentagon said a Chinese intelligence collection ship challenged the Impeccable over the radio, calling its operations illegal and directing the vessel to leave the area or "suffer the consequences".

Because the vessels' intentions were not known, Impeccable sprayed its fire hoses at one of the vessels in order to protect itself, the Pentagon statement said.

Safe path request

The US ship's commander asked the Chinese ships by radio "in a friendly manner" for a safe path to leave the area.

Two Chinese boats then moved directly in front of the Impeccable, forcing it to take emergency action to avoid collision, said the statement.

The Pentagon said the encounter was the latest incident of "increasingly
aggressive" Chinese conduct in the area.

Major Stewart Upton, a Pentagon spokesman, said: "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.

"We expect Chinese ships to act responsibly and refrain from provocative activities that could lead to miscalculation or a collision at sea."