BEIJING — China demanded that Vietnam withdraw ships from disputed waters around a Chinese 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 that Vietnamese ships had rammed Chinese vessels as many as 171 times over four days. The announcement followed accusations by Vietnam on Wednesday that Chinese ships had rammed its vessels early this week and sprayed the Vietnamese flotilla with water cannons.
The Chinese, who on Thursday admitted to the use of water cannons, say Vietnam has dispatched 35 ships to the area, while the Vietnamese have said the Chinese deployed about 80 vessels.
The movement of the drilling rig follows recent attempts by China to solidify its increasingly muscular claims over both the South China Sea, one of the world’s major trading routes, and the East China Sea.
In November, Beijing declared an air defense zone over a swath of the East China Sea, including islands that both China and Japan claim, and demanded that other countries notify the 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 disputes have raised concerns in Washington, 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.
On Thursday, the U.S. assistant secretary of state for East Asian and Pacific Affairs, Daniel R. Russel, who was on a trip to Hanoi, Vietnam, said 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.”