VIETNAM demanded today that China stop oil drilling operations in a disputed patch of the South China Sea.

The Vietnamese foreign ministry insisted that Beijing’s decision to deploy a deep-sea rig over the weekend was illegal.

China’s claims of sovereignty in potentially oil- and gas-rich waters have raised tensions with Vietnam, the Philippines and other countries.

The China Maritime Safety Administration posted a navigational warning on its website advising that an oil rig would be drilling in the South China Sea from May 4 to August 15 in an area close to the Paracel Islands, which are controlled by China but which Vietnam claims as its own.

China’s maritime administration added that ships were banned from waters within three miles of the rig.

But Vietnam’s foreign ministry insisted that 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. “Vietnam resolutely protests them.”

Vietnam’s state-owned oil company PetroVietnam demanded that the China National Offshore Oil Corporation “immediately stop all the illegal activities and withdraw the rig from Vietnamese waters.”

Asked about Vietnam’s objections, Chinese Foreign Ministry spokeswoman Hua Chunying insisted that the drilling was taking place in Chinese waters.

Vietnam has also accused Chinese ships of cutting cables to its exploration vessels and harassing fishermen, as has the Philippines.