U.S. officials said on Tuesday that China had tested multiple anti-ship ballistic missiles from man-made structures near the Spratly Islands of the disputed waters over the weekend.

Pentagon spokesman Lieutenant Colonel Dave Eastburn was quoted by NBC News as saying that the tests represented a "truly disturbing" violation of President Xi Jinping’s 2015 statement that China "does not intend to pursue militarization" in the water body.

Earlier, the China Maritime Safety Administration announced that Chinese naval forces would be conducting a series of anti-ship ballistic missile tests in an area to the north of the Spratlys from June 29 until July 3. It asked all fishing boats not to travel into the 22,500-square-kilometer area during the exercise.

Le Thi Thu Hang, spokeswoman of Vietnam's Ministry of Foreign Affairs, told the press on Thursday that "Vietnam is extremely interested and is closely following the incident."

Vietnam demands all activities of the involved parties in the South China Sea, which Vietnam calls the East Sea, must respect the sovereignty and legal and legitimate rights of countries in accordance with international law, especially the United Nations Convention on the Law of the Sea (UNCLOS), Hang said.

"Activities must contribute to peace, security, stability and cooperation in the region," she said.

China seized the Paracel Islands from South Vietnam by force in 1974, and has been illegally occupying a number of reefs in the Spratly Islands since 1988.

Vietnam has full legal basis and historical evidence to assert its sovereignty over the Paracel and Spratly Islands and its waters in accordance with international laws.