Vietnamese and Chinese ships clashed over the weekend in a disputed area of the South China Sea as Vietnam attempted to prevent China from setting up an oil rig in waters claimed by both countries.

Rear Adm. Ngo Ngoc Thu, vice commander of Vietnam’s coast guard, told the Associated Press Wednesday that Chinese ships on Sunday rammed Vietnamese vessels and sprayed them with water cannons. Thu said a number of ships were damaged in the incident and several sailors were injured.

China stationed the oil rig over the weekend in an area of the South China Sea close to the Paracel Islands as part of a move to assert control of disputed waters that are also claimed by Vietnam, the Philippines and other Southeast Asian nations. The clash between Vietnam and China was the most serious in years between the two countries at sea.

The incident led Vietnam to dispatch as many as 29 naval and coast guard ships to waters close to the oil rig. A Chinese diplomat told the AP that a Vietnamese diplomat told him the move was a way to be a “show of force” and get China to back down from setting up the rig in a “fixed position.”

China says it acted appropriately, with Foreign Ministry spokeswoman Hua Chunying saying that the oil rig is in its territorial waters. She said the drilling is “normal and legal.”

The United States said it is concerned about China’s actions surrounding the oil rig. U.S. State Department spokeswoman Jen Psaki called Beijing’s moves “provocative and unhelpful to the maintenance of peace and stability in the region.”

Hua responded to the U.S. statement, saying, “We want to tell the U.S. that the U.S. has no right to make irresponsible and unwarranted remarks on China's sovereign rights.”

Vietnam’s “back is against the wall” as it deals with China over the dispute, according to one expert.

"China seems intent on putting down its footprint squarely in contested waters and force Hanoi's hand. It appears a critical juncture has occurred and one would expect Hanoi to be weighing its options," Jonathan London, a Vietnam expert at the City University of Hong Kong, told the AP. “Hanoi's back is against the wall, though China's policies — which according to virtually everyone except China are baseless legally — have brought about this situation.”

The dispute between Vietnam and China occurred a day after Beijing clashed with the Philippines after Manila detained 11 Chinese fishermen on charges of catching endangered sea turtles in the South China Sea.