Itsunori Onodera's comments are likely to further heighten fears that the two countries could be sliding towards conflict over the outcrops in the East China Sea and come on the day that China showed off its fleet of nuclear-powered submarines.
"I believe the intrusions by China in the territorial waters around the Senkaku islands fall in the 'grey zone' (between) peacetime and an emergency situation," Onodera told reporters in Tokyo.
But the comments from Onodera following those from China's defence ministry at the weekend, appear to have taken the verbal fisticuffs to a new level.
China's coastguard yesterday sent four vessels into the waters around the islands, where they stayed for two hours, shadowed by their Japanese counterparts.
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That came after three consecutive days in which Tokyo scrambled jets to meet Chinese aircraft as they traversed a strait leading to the Pacific. They did not enter Japanese airspace.
"It was unusual that so many aircraft flew between the Okinawan main island and Miyako island. We consider that it is also very unusual that it occurred for three days in a row.
"We understand that it is one of the trends showing that China is now vigorously expanding its areas of activities, including into the open ocean.