Dec. 3 (UPI) -- China is defending its actions in the East China Sea after Japan filed a complaint, following China's decision to launch an offshore gas exploration project.
Chinese foreign ministry spokesman Geng Shuang said Monday there are no grounds for the Japanese complaint.
Geng confirmed China is conducting oil and natural gas exploration, but the projects are taking place on the Chinese side of the East China Sea.
Japanese officials said the drilling was taking place near a "median line" that separates the countries' exclusive economic zones, Kyodo News reported Monday.
Geng said a median line was never recognized, and that China completely objects to Japan's "unilateral claim."
Earlier in the day, Japanese Chief Cabinet Secretary Yoshihide Suga expressed "regret" over Chinese actions.
"It is extremely regrettable that China has continued its unilateral development activities in the waters, while the boundary [between Japan and China] has not been fixed," Suga told reporters in Tokyo.
Japan's self-defense forces were the first government agency to confirm Chinese movements in the East China Sea, according to Japanese officials.
The officials said the exploration began around mid-November about 75 miles from Japan's claimed demarcation line.
In 2008, the two countries agreed on joint gas development, but the deal fell through in 2010, owing to increased friction over territorial claims in the East China Sea.
Since that time China has installed 16 gas exploration facilities in the East China Sea.