“Vietnam is very worried about this information,” Le Hai Binh,Vietnam’s Foreign Ministry spokesman, said in a statement issued late Friday, adding that the Spratly islands rightfully belonged to Vietnam.

China has installed anti-aircraft guns and other weapons systems on each of seven artificial islands constructed by it in the archipelago, according to a report published on Tuesday by the US think tank the Asia Maritime Transparency Initiative.

The construction works shows “that Beijing is serious about defence of its artificial islands in case of an armed contingency in the South China Sea,” the report said.

“Among other things, they would be the last line of defence against cruise missiles launched by the United States or others against these soon-to-be-operational air bases,” it continued.

Vietnam, Malaysia, the Philippines, Taiwan and Brunei all have competing claims with China in the South China Sea.