A top defense official has warned that China may be creating artificial islands in the disputed South China Sea as a forerunner to declaring an air defense identification zone (ADIZ) over the waters.

"China is building islands in the South China Sea on which to put radar and air defense missiles," Masanori Nishi, a policy adviser to Defense Minister Gen Nakatani, said in an opinion piece published Monday in Defense News, a U.S. weekly publication.

The initiative "might be for a future ADIZ announcement in the South China Sea," said Nishi, who took up his current post in October after resigning as vice defense minister, the top bureaucrat in the Defense Ministry.