BEIJING — China demanded that Vietnam withdraw ships from disputed waters near a Chinese oil-drilling rig Thursday, the latest volley in a standoff that has quickly escalated into one of the most serious in years in the contested South China Sea.
The latest tensions began last week, when a state-owned Chinese energy company moved the rig into position and intensified as ships sent by both countries faced off against each other.
On Thursday, a Chinese Foreign Ministry official said Vietnamese ships had rammed Chinese vessels up to 171 times over four days. The announcement followed accusations by Vietnam on Wednesday that Chinese ships had rammed its vessels earlier in the week and sprayed the Vietnamese flotilla with water cannons.
The Chinese, who Thursday admitted using water cannons, say Vietnam has sent 35 ships to the area, while the Vietnamese have said the Chinese deployed about 80 vessels. The rig is about 17 nautical miles from disputed islands known in Vietnam as the Paracel Islands and in China as the Xisha.
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The movement of the drilling rig follows recent attempts by China to solidify its increasingly muscular claims over the South China Sea, one of the world’s major trading routes, and the East China Sea.
In November, China’s government declared an air-defense zone over a swath of the East China Sea, including islands that China and Japan claim, and demanded that other countries notify Chinese authorities before their planes pass through the airspace.
Although the U.S. military and Japanese aircraft flouted the demands, analysts have suggested the air-defense zone helps China build its case for taking over the disputed islands, which Japan controls.
China has also appeared to tighten its hold over a reef called Scarborough Shoal in the South China Sea, which the Philippines claims.
The oil-rig stalemate underlines the apparently intractable nature of many of China’s territorial disputes with its neighbors, and it has raised the possibility of a conflict in the South China Sea’s most serious incident in years.
Vietnam’s main stock-market index recorded its biggest one-day drop since 2001 on fears of a protracted stalemate or possible conflict between the neighboring nations, which have fought two naval skirmishes in the waters since 1974 and have history of conflict going back 1,000 years.
China’s conflicts with neighbors center in part on a competition for natural resources, including what some believe are substantial deposits of oil and gas beneath the seabed. China has been particularly eager to find energy reserves to feed its growing industrial needs.
The oil rig in the South China Sea was stationed by China National Offshore Oil Corp., or CNOOC, 120 nautical miles off the Vietnamese peninsula.
Yi Xianliang, deputy director general of the department of Boundary and Ocean Affairs of China’s Foreign Ministry, who acknowledged Thursday that China had used water cannons against Vietnamese ships, said: “They are the most gentle measure we can take when trying to keep the other side out.”
He added that China’s oil-drilling operations were legal because they were in “China’s inherent territory.”
China is prepared to negotiate with Vietnam to resolve the dispute, Yi said, but first Vietnam must end its “disruption” and must remove its vessels. There have been 14 “rounds of communication” between the two sides in the past few days, Yi added.
The rig is capable of drilling to a depth of 10,000 feet, according to Li Yong, chief executive of China Oilfield Services, who attended the briefing with Yi. China plans to drill while the area is typhoon-free in May, June and July.
Ngo Ngoc Thu, deputy commander of Vietnam coast guard, said the situation remained tense but there had been no contact Thursday. “The two sides are still shadow boxing with each other,” he said.
China has been increasingly pressing its claims in the South China Sea, which it claims almost in its entirety. In addition to Vietnam and the Philippines, this stand is bringing China into conflict with Malaysia, Brunei and Taiwan, which also claim parts of the waters.
China’s disputes with neighbors have raised concerns in the U.S., which has been trying to carefully calibrate its response to the various territorial claims. The Obama administration has courted countries in Southeast Asia as a counterbalance to China’s power, but it has also been trying not to antagonize the Chinese.
The U.S. Assistant Secretary of State for East Asian and Pacific Affairs, Daniel Russel, who was visiting Hanoi, Vietnam, said Thursday that the latest dispute had been a major topic of his discussions there.
“We oppose any act of intimidation by vessels, particularly in disputed areas,” he said. The United States did not take a position on the competing claims of sovereignty, he added, but the disputes need to be “dealt with diplomatically and must be dealt with in accordance to international laws.”
Material from The Associated Press is included in this report.