Each day the Vietnamese ships tried to get close to the rig. And each day they were driven back by the much larger Chinese ships.

But before they sped away, laboring engines spewing black smoke, the Vietnamese delivered a message: "Attention! Attention! We are warning you about your provocative act," blasted out a recording from a loudspeaker in Vietnamese, Chinese and English. "We demand you respect Vietnam's sovereignty. Please immediately halt your activities and leave Vietnamese waters."

Occasionally colliding with or firing water cannons at each other, Vietnamese and Chinese ships have been shadow boxing in a sun-dazzled patch of the South China Sea since May 1, when Beijing parked a hulking, $1 billion deep sea oil rig, drawing a furious response from Vietnam.

Vietnam, ten times smaller than its northern neighbor and dependent on it economically, needs all the help it can get in the dispute. Its leaders believe international opinion is on their side. This week they invited foreign journalists to get a closer look at the standoff, the most serious escalation between the countries in years over their overlapping claims.

Vietnam is determined to defend what it regards as its sovereign territory against China, which insists that most of the South China Sea — including the Paracel Islands it took from U.S.-backed South Vietnam in 1974 — belongs to it. But Hanoi lacks options in dealing with Beijing, as China uses it burgeoning economic and military might to press its claims in the seas.

Vietnam has accused Chinese vessels of deliberately and dangerously ramming its ships. TV footage recorded last week from a Vietnamese ship showed a Chinese vessel smashing into the stern of the Vietnamese ship then backing up and ramming it again, damaging its side. The Chinese Ministry of Foreign Affairs on Friday released three photographs purportedly showing a Vietnamese vessel ramming a Chinese maritime ship. The media onboard this week did not witness any ramming.

"It is not that we want to be in confrontation with the Chinese, but it's our duty to carry out daily patrols in Vietnamese territory," said Col. Le Trung Thanh, the skipper of the Vietnamese coast guard ship 4033. "We want to get close to the rig to persuade them that their actions are illegal and they must leave Vietnam's water unconditionally."

That seems unlikely, however many patrol boats Hanoi sends to the area, or pleads its case to the world. For China, a withdrawal would signal weakness.

Beijing has said it plans to keep the rig until August. While most analysts think neither side has any interest in an armed conflict, the longer the confrontation lasts, the greater the risk of an unplanned incident that could lead to a shooting match.

China has set up a 10-kilometer (6.21-mile) exclusion zone around the rig, which was visible on the horizon. On occasion, Chinese surveillance planes flew over the Vietnamese vessels. Both sides have deployed dozens of vessels, mostly coast guard and fisheries protection fleets. At least one of the Chinese ships had cannons, which were uncovered.

In 1974, China ousted the South Vietnam navy from the Paracel Islands, close to where the rig is currently deployed, killing 75 South Vietnamese sailors. The two countries fought a brief but bloody border war in 1979. In 1988, 64 Vietnamese sailors were killed in another skirmish in the nearby Spratly Islands, where territorial spats between China and the Philippines have recently heated up.

As the latest standoff plays out on high seas, Hanoi's Communist government has been struggling to contain rising popular anger against China, never far from the surface in Vietnam. Protesters this week vandalized foreign-owned factories and killed at least one Chinese national, further inflaming the situation.

Beijing has accused Hanoi of not doing enough to stop the violence. On Friday, it criticized Vietnam for organizing the media trip.

"It is clear that the aim of the Vietnamese side is to escalate the situation and create tension, or in other words, to generate media hype and put up a show in front of the international audience," said Ouyang Yujing, the director general of the Chinese Foreign Ministry's Department of Ocean and Boundary Affairs.

Vietnam's Communist Party has been trying to leverage its links with the party in China to quietly resolve their differences, mindful of the economic importance of good relations. Just last month, one of the coast guard ships stationed close to the rig took part in joint fishery patrols with Chinese vessels in the Gulf of Tonkin, said Vietnam's coast guard Col. Dinh Quoc Ruan.

Unlike in the Paracels, the two countries settled their maritime border in the Gulf of Tonkin in 2000.

Crew members boarded each other's boats to share fruit with each other and take photos, Ruan said.

"I'm not surprised when the Chinese switched from being friends to being opposed so quickly," he said. "Being friends with China is not so easy."

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Associated Press writers Chris Brummitt in Hanoi, Vietnam, and Jack Chang in Beijing contributed to this report.