China firmly opposes any construction activities by the Philippines on Chinese islands and reefs in the South China Sea that are illegally occupied by the Philippines, a Chinese defense spokesperson said on Monday.

Jiang Bin, a spokesperson for China's Ministry of National Defense, made the remarks in response to reports that satellite imagery showed the Philippines accelerating infrastructure construction on illegally occupied islands and reefs in the Nansha Islands.

"China has indisputable sovereignty over the Nansha Islands and their adjacent waters," Jiang said at a press briefing.

"We firmly oppose the Philippine side carrying out construction activities on illegally occupied Chinese islands and reefs, including Zhongye Dao and Mahuan Dao," he said.

Jiang added that China will take necessary measures to safeguard its territorial sovereignty and maritime rights and interests.