Satellite images were released by the Asia Maritime Transparency Initiative (AMTI) showing that artificial islands are being developed to shelter surface-to-air missiles.
The Washington-based think tank showed that the structures are now built on Fiery Cross Reef, Mischief Reef and Subi Reef in the Spratly Islands. All these islands are still being disputed by neighboring Asian countries.
The think tank said that China is showing continuous efforts for South China Sea militarization and do not necessarily indicate a reaction to the changes in U.S. politics.
The report stated, "This indicates they are not reactions to the political cycle in Washington, but rather part of a steady pattern of Chinese militarization."
The structures were constructed in September and November last year. China created seven artificial islets from the sea's existing reefs.
The satellite photos are contrary to the statements given by China that they do not intend to use the South China Sea as a military area. The pictures also showed that China is building runways and other military equipment.
Other foreign leaders have expressed concern that China is still militarizing the disputed shoals. The foreign ministers of the Association of Southeast Asian Nations said the structures may raise tensions among Asian countries.
Philippine Foreign Affairs Secretary Perfecto Yasay said, "A number of ministers expressed concern over recent developments and escalation of activities in the area, which may further raise tensions and erode trust and confidence in the region."
Yasay spoke at the foreign ministers' meeting in Boracay.
He also mentioned that the United States sent USS Carl Vinson in the waters of the South China Sea, as part of their routine operations.
Yasay said, "Asean member countries underscored the importance of the full and effective implementation of the Declaration of Conduct (DOC) on the South China Sea in its entirety."