Vietnam has accused China of threatening safety of civilian flights over the disputed South China Sea by failing to properly inform its aviation authorities of Beijing's recent test flights to a man-made island also claimed by Hanoi.

Vietnamese Foreign Ministry spokesman Le Hai Binh said that although a Chinese Embassy representative did inform the Vietnamese Foreign Ministry about the flights last month, prompting a protest from Hanoi, that did not extend to the Civil Aviation Authority of Vietnam and threatened the safety of civil aviation.

The notification from the Chinese Embassy "cannot substitute China's notification to the appropriate air traffic services units of Vietnam in order to ensure the safety and regularity of flight operations," the Civil Aviation Authority of Vietnam said in a statement late Tuesday.

China Foreign Ministry spokesman Hong Lei told reporters Monday that China's three test flights to Fiery Cross Reef — one of seven South China Sea features where China had carried out extensive land reclamation — were state aviation activities and had no restrictions under international law.

Hong said that Beijing informed Vietnamese aviation authorities on Dec. 28 and Foreign Ministry two days later about them. He said that Vietnam had failed to see "the professional, technical and civil nature of China's inspection and test flights."

Vietnamese Foreign Ministry spokesman Le Hai Binh disputed Hong and said that at the meeting with the Chinese Embassy representative, Vietnam protested and demanded that China cancel the flights.

Binh said the flights violated Vietnam's sovereignty over the islands, and demanded that China stop any such activities.

Vietnam and China both claim the Paracel Islands and the two along with the Philippines, Malaysia, Brunei and Taiwan claim all or parts of the Spratlys, which sit on potentially oil and gas rich resources and occupy one of the world's busiest shipping lanes.

China's recent increasing assertiveness has caused serious concerns among its neighbors and the United States, which backs freedom of navigation and overflights in the South China Sea.