At one point during the incident Sunday the unarmed USNS Impeccable turned fire hoses on an approaching Chinese ship in self defence, the Pentagon said. At another point a Chinese ship played chicken with the Americans, stopping dead in front of the Impeccable as it tried to sail away, forcing the civilian mariners to slam on the brakes.

"We view these as unprofessional manoeuvres" and a violation of international law, Pentagon spokesman Bryan Whitman said.

The incident had overtones of spycraft, but the US ship is not, strictly speaking, a spy ship. It maps the ocean floor with sonar, compiling information the Navy can use to steer its own submarines or track those of other nations.

The Impeccable was specifically designed to augment the Navy's anti-submarine capability, although military spokesmen would not be specific about the ship's duties when it was surrounded.

A Pentagon accounting of the confrontation documents the actions of the startled and cornered American crew as a Chinese vessel closed to within 25 feet. Pictures released by the Navy give a sense of the surreal scene: The Chinese mariners had stripped to their underwear following the blast by the Impeccable's fire hoses.

Whitman called that "immature," and said the confrontation was the most aggressive of a series of incidents recently in the same area.

Impeccable's crew radioed to tell the Chinese ships that it was leaving the area and requested a safe path to navigate, the Pentagon said.

But two of the Chinese ships stopped directly ahead of the Impeccable, forcing it to an emergency stop, the US account said. The Chinese also dropped pieces of wood in the water in Impeccable's path.

The incident came just a week after China and the US resumed military-to-military consultations following a five-month suspension over US arms sales to Taiwan. And it came as Chinese Foreign Minister Yang Jiechi was due in Washington to meet with U.S. officials.

"We're going to continue to operate in those international waters, and we expect the Chinese to observe international law around that," White House press secretary Robert Gibbs said.

A protest was lodged with the Chinese government by the US Embassy in Beijing over the weekend and was repeated to a Chinese defence attache at a Pentagon meeting Monday.

In Beijing, Chinese officials did not immediately respond to voicemail messages and e-mail regarding the US allegations.

Pentagon officials said the incident followed "increasingly aggressive" acts by Chinese ships against the Impeccable on Wednesday and Saturday and against the USNS Victorious surveillance ship on Thursday while it operated in the Yellow Sea.

The Chinese ships included a Chinese Navy intelligence collection ship, a Bureau of Maritime Fisheries Patrol Vessel, a State Oceanographic Administration patrol vessel and two small Chinese-flagged trawlers, officials said.

China views almost the entirety of the South China Sea as its territory. China's claims to small islets in the region have put it at odds with five governments - the Philippines, Vietnam, Malaysia, Brunei and Taiwan.

Pentagon officials said the close encounter followed these other incidents last week:

• On Wednesday, a Chinese Bureau of Fisheries Patrol vessel used a high-intensity spotlight to illuminate the Victorious, an ocean surveillance ship, as it operated in the Yellow Sea, about 125 nautical miles from China's coast, the Pentagon said. The next day, a Chinese Y-12 maritime surveillance aircraft conducted 12 fly-bys of Victorious at an altitude of about 400 feet and a range of 500 yards.

• On Thursday, a Chinese frigate approached USNS Impeccable without warning and crossed its bow at a range of approximately 100 yards, the Pentagon said. This was followed less than two hours later by a Chinese Y-12 aircraft conducting 11 fly-bys of Impeccable at an altitude of 600 feet and a range from 100-300 feet.

• On Saturday, a Chinese intelligence collection ship challenged Impeccable over bridge-to-bridge radio, calling her operations illegal and directing Impeccable to leave the area or "suffer the consequences."