China has "indisputable sovereignty" over the Spratly and Paracel islands, Foreign Ministry spokeswoman Jiang Yu said, rejecting recent comments from Vietnam, which also asserts dominion over the islands believed to sit above large oil and natural gas reserves in strategic shipping lanes.

Chinese forces seized the western Paracels from Vietnam in 1974 and sunk three Vietnamese naval vessels in a 1988 sea battle. The sides have yet to demarcate their sea border and many Vietnamese remain suspicious of their giant northern neighbor.

Vietnamese Foreign Ministry spokeswoman Nguyen Phuong Nga on Monday protested a Chinese plan to develop tourism in the region, saying it "seriously violates Vietnam's sovereignty ... causes tension and further complicates the situation."

That followed the Chinese Cabinet's unveiling of plans Monday to transform the southern island of Hainan into a major international tourism destination over the next decade and expand oil and natural gas exploration in the area.

The announcement did not specifically mention the Paracel and Spratly island chains, but China says they fall under Hainan's administration.

China and Vietnam both cite historical and archaeological evidence to back up their claims to the islands, and China has increasingly sought to cement its hold through international maritime law.

Taiwan, Malaysia, Brunei, and the Philippines also claim all or part of the Spratlys.