Japan is protesting what is says was an unauthorized Chinese maritime survey within its economic waters near disputed East China Sea islands.

Japan's Foreign Ministry says it lodged a protest with Beijing after a Chinese maritime research ship was seen dropping a wire-like object into the water off the northwestern coast of Japanese-controlled Senkaku islands on Sunday.

China also claims the islands, which it calls Diaoyu.

The ministry said Monday it urged China to immediately stop the survey.

Also Monday, Japan's coast guard says four Chinese patrol ships violated Japanese territorial waters off the Senkaku.

Japan's Defense Ministry says a Chinese frigate was spotted Sunday near the Miyako Strait, and a Chinese reconnaissance aircraft was flying above the East China Sea. The latter prompted Japan to scramble a fighter jet.