China has demanded that Vietnam withdraw its ships from a part of the disputed South China Sea where a Chinese firm is establishing an oil rig, and accused Vietnamese vessels of ramming Chinese ships in the area.
After the latest confrontation between vessels from the two countries, a senior Foreign Ministry official in Beijing said China was "shocked" at the "provocations of Vietnam" and vowed the drilling in the disputed Paracel Islands would continue.
"Vietnamese vessels are colliding intentionally with Chinese vessels carrying out normal operations, trying to disturb and stop the drilling work by Chinese," said Yi Xianliang, deputy director general of the ministry's boundary and ocean affairs department. He also warned Washington not to interfere, referring to remarks by US officials about "dangerous conduct and intimidation by vessels" in the area.
"The remarks by US officials have pushed some parties to resort to provocations," Yi said. "This is a matter between China and Vietnam, and has nothing to do with any other third party."
Daniel Russel, US assistant secretary of state for East Asia and the Pacific, who was in Hanoi, reiterated Washington's concerns.
"It's within the rights of the United States and the international community to call all parties to address the dispute in a peaceful way," Russel said.
Tensions flared on Saturday when Beijing announced the drilling off Triton Island, known as Zhongjian Island in China. Hanoi said the drilling was illegal and sent patrol vessels. On Wednesday, Hanoi said Chinese vessels had used water cannon to attack Vietnamese law enforcement vessels.
Yi said using water cannon was the "most restrained measure" that could be taken and China had to send more ships, as its vessels had suffered 171 clashes with 35 Vietnamese vessels.
"Vietnam is sending more and more ships to the area," Yi said. "We need to have some forces around to avoid unnecessary loss and ensure a safe environment for the drilling operation."
Vietnam said China had stationed about 80 ships around the rig, seven of them military. Yi declined to say how many Chinese vessels were deployed, but said none was military.
He said China had been drilling in the area for more than 10 years, and the location, 17 nautical miles from China and 130 to 150 nautical miles from Vietnam, was under the administration of Sansha in the Paracels, which China declared a prefecture-level city in 2012.
"China has indisputable sovereignty over there," Yi said.
He said Beijing would resolve the dispute through diplomatic channels. Officials from the two nations have met 14 times in recent days.
Li Yong, chief executive officer of the China National Offshore Oil Corporation, which is conducting the drill, said the Vietnamese vessels posed a serious danger to Chinese workers.