Vietnam protested a Chinese decision to begin drilling for oil in disputed waters of the South China Sea, calling the move illegal yesterday and demanding Beijing pull back from the area.
Beijing's deployment of its first deep-sea rig was the latest in a series of provocative actions aimed at asserting its sovereignty in the sea that have raised tensions with Vietnam, the Philippines and other claimants.
The United States shares many of the regional concerns about China's actions in the sea, which is potentially rich in gas and oil. Last week, US President Barack Obama signed a new defence pact with the Philippines aimed at reassuring allies in the region of American backing as they wrangle with Beijing's growing economic and military might.
The Maritime Safety Administration of China (MSAC) posted a navigational warning on its website on Saturday advising that the China National Offshore Oil Corporation (CNOOC) 981 rig would be drilling in the South China Sea from May 4 to August 15, in an area close to the Paracel Islands, 800 kilometres south west of Hong Kong. The islands are controlled by China but Vietnam claims them as its own.
The warning by MSAC initially said a 1.6-kilometre exclusion zone for all other vessels was being imposed around the rig. Yesterday, that exclusion zone was increased to 4.8 kilometres, MSAC said.
Vietnam's foreign ministry said the area where the rig was stationed lay within Vietnam's exclusive economic zone and continental shelf as defined by the 1982 UN Convention on the Law of the Sea.
"All foreign activities in Vietnam's seas without Vietnam's permission are illegal and invalid," the ministry said in a statement. "Vietnam resolutely protests them."
Vietnam's state-owned oil company, PetroVietnam, demanded that CNOOC "immediately stop all the illegal activities and withdraw the rig from Vietnamese waters."
Chinese Foreign Ministry spokeswoman Hua Chunying , asked about Vietnam's protest, said the rig was operating "completely within the waters of China's Paracel Islands". She declined to elaborate.
Many analysts believe China is embarking on a strategy of gradually pressing its claims in the water by seeing what it can get away with, believing that its much smaller neighbours will be unable or unwilling to stop it. Vietnam has accused Chinese ships of cutting cables to its exploration vessels and harassing fishermen, as has the Philippines.
Chinese assertiveness puts Vietnam's authoritarian government in a difficult position domestically because anger at China, an ideological ally, runs deep in the country. This is exploited by dissident movements, who accuse the government of being unwilling to speak out against Beijing.
Tran Cong Truc, the former head of a government committee overseeing the country's border issues, said the latest Chinese move was especially provocative.
"This act by China is much more dangerous than previous actions such as cutting the exploration cable or fishing bans," he said.
CNOOC, China's top offshore oil producer, in 2012 invited foreign companies to jointly develop nine blocks in the western part of the South China Sea, a move Vietnam said was illegal because the blocks overlap its territorial waters.