Japan's government has lodged a protest with China over drilling activity in the waters between the two countries.

Japanese Foreign Minister Fumio Kishida said Tuesday that Japan had confirmed that a moored Chinese drilling ship is conducting some kind of activity in the East China Sea.

He called China's oil and gas exploration efforts "extremely regrettable" at a time when the maritime boundaries between Japan and China have not been established.

Japan has complained about similar activity before, largely in the waters between the Chinese mainland and Okinawa and other southern Japanese islands.

The two countries also are entangled in a dispute over a group of uninhabited islands that they both claim farther south in the East China Sea.