The Defense Agency said Friday the intrusion of a Chinese submarine into Japan's territorial waters was a highly provocative act by the Chinese Navy.

Agency officials speculated that the Chinese military was trying to use the brief trespass Wednesday to show off its sea power.

They said it was probably an attempt to intimidate Japan and help Beijing's efforts to secure greater resources in the East China Sea, as well as to keep in check the U.S. forces that watch over Taiwan.