Vietnamese Foreign Ministry spokeswoman Le Thi Thu Hang told reporters that her government has legal basis and historical evidence to affirm its sovereignty over the Spratly and Paracel islands in the South China Sea and that acts by foreign countries on the islands without Vietnam's permission were illegal.
"It's our view that China as a major power in the region and in the world needs to act in responsible and constructive manner in maintaining peace, stability in the region as well as in the East Sea on the basis of respecting international law," she said, referring to the South China Sea.
Once complete, the report said China will be able to house up to three regiments of fighters in the Spratly Islands.
China has also built up infrastructure on the four smaller outposts, including land-based guns and communications facilities, the report said.
Vietnam, along with China and the Philippines, Malaysia, Brunei and Taiwan claims parts of or all the Spratly islands, which are believed to sit on rich natural resources and occupy one of the world's busiest sea lanes.