China on Thursday said its marine surveillance plane flying over the Diaoyu Islands was "completely normal."

"The Diaoyu Island and its affiliated islets are an inalienable part of China's territory, and it's completely normal for a Chinese marine surveillance plane to fly over them," Chinese Foreign Ministry spokesman Hong Lei told a regular press conference.

He also urged Japan to stop its illegal operations in the waters and space concerning the islands.

Hong pointed out that the current severe difficulties in China-Japan relations are the result of Japan's illegal purchase of the Diaoyu Islands, and he called on the Japanese government to correct its mistakes by showing sincerity and taking action through dialogue and negotiations.