The Center for Strategic and International Studies said satellite images seemed to show large anti-aircraft guns, anti-missile systems and radar facilities on the reclaimed islands in the South China Sea, which are also claimed by Taiwan, Vietnam and the Philippines.

Western defence analysts said such defences would represent a serious deterrent against attack by the US or other nations and that the images further undermined the claim by Chinese President Xi Jinping last year that Beijing did not intend to “militarise” the islands.

The latest claim about Beijing’s assertive activities in the South China Sea comes at an uncertain time for US-China relations, with President-elect Donald Trump threatening to take a tougher line with China on trade, Taiwan and the South China Sea.