BEIJING, May 7 (Xinhua) -- China said on Wednesday that operation of its drilling rig 981 near the Xisha Islands in the South China Sea is legal and urged Vietnam to stop disturbing China's exploration activities in its territorial waters.

Foreign Ministry Spokeswoman Hua Chunying made the remarks at a regular press conference.

The Maritime Safety Administration of China issued navigational notice about rig 981, which belongs to China National Offshore Oil Corporation (CNOOC), on May 3, she said, adding that operation of the drilling rig is lawful in China's territorial waters.

She said Vietnamese harassment of Chinese companies conducting normal activities runs counter to international law and basic norms of international relations as well as China's sovereignty and administration rights.

China's State Councilor Yang Jiechi had a phone conversation with Vietnam's Deputy Prime Minister and Foreign Minister Pham Binh Minh on Tuesday, demanding that the Vietnamese side stop disturbing Chinese companies' normal work in the Xisha Islands.

The United States on Tuesday criticized China by calling its exploration activities "provocative and unhelpful to the maintenance of peace and stability in the region."

Hua said the Xisha Islands are part of China's inherent territory and the activities of the Chinese companies in the Xisha Islands are within the mandate of China's sovereignty and administration, which have nothing to do with Vietnam and the U.S.

She said the U.S. is in no position to make irresponsible remarks on China's affairs.