Japan has asked China to stop drilling for gas in a disputed area along the two countries' sea border in the East China Sea.
A Japanese foreign ministry official said Wednesday, that his country deeply regrets China's one-sided decision to start extracting natural gas from the region.
Beijing does not recognize Tokyo's territorial claims in the area west of Japan's southernmost islands. However, it is not clear if the drilling is within what Japan considers its exclusive economic zone.
On Tuesday, China said it was within its rights to continue drilling in the area, but was willing to negotiate with Japan over the territorial waters.
Some information for this report provided by AP and Reuters.