Chief Cabinet Secretary Yoshihide Suga said Monday that Japan has been protesting China's construction of new gas field development facilities in the East China Sea since June 2013.

"We have repeatedly protested against China's unilateral gas development and have urged China to stop it," Suga said of the facilities, which are near the Japan-proposed boundary between the two countries' exclusive economic zones.

Japan and China have not agreed on a boundary in the East China Sea where their 200-mile EEZs overlap. While Japan has proposed a median line in the overlapping zone, China insists on a wider Chinese EEZ.