China defended its patrol boats' activities in waters near the Diaoyu Islands on Wednesday, adding they were on a normal patrol mission to protect Chinese fishermen.

"Our law enforcement vessels patrolled the waters to maintain normal order for our fishing vessels. China has made its stance regarding the issue clear to the Japanese side," Foreign Ministry spokesman Ma Zhaoxu said in a press release.

The press release came in response to media query about a complaint issued by Japan earlier Wednesday after two Chinese ships entered waters within 12 nautical miles of the Diaoyu Islands.

"China has indisputable sovereignty over the Diaoyu Islands and its adjacent islets, which have been an integral part of Chinese territory since ancient times," Ma said.