BEIJING - China said on Tuesday that it is an exercise of its legitimate sovereignty for relevant Chinese ships to conduct normal marine research in the waters near Diaoyu Island.

Foreign Ministry spokesman Hong Lei made the remarks at a daily press briefing when asked to comment on China's recent scientific survey activity in the waters near Diaoyu Island.

"Diaoyu Island and its adjacent islands have been Chinese territory since ancient time, and China has indisputable sovereignty over them," Hong added.