China on late Friday opposed Japan's naming of five islets belonging to the Diaoyu Islands, saying the move is illegal and invalid.
"China resolutely opposes Japan's move to undermine its territorial sovereignty as the Diaoyu Island and its affiliated islands are China's territory and have been already named by the country," Foreign Ministry spokesman Qin Gang said in a statement.
According to China's news agency Xinhua, Qin's comments came hours after Japan named five isles belonging to the Diaoyu Islands.
"Japan's unilateral measure is illegal and invalid and cannot change the fact that the Diaoyu Island and its affiliated islands are part of China's territory," the spokesman said.
China-Japan relations have soured since the Japanese government's "purchase" of the Diaoyu Islands in September 2012.