That agreement saw Japan and China agree to jointly develop undersea gas reserves in the disputed area, with a ban on independent drilling by either country.

But negotiations over how to implement the deal were suspended in 2010.

Japan has long insisted the median line between the two nations should mark the limits of their respective EEZs.

China, however, insists the border should be drawn closer to Japan, taking into account the continental shelf and other ocean features.

The two countries are embroiled in a separate row over disputed islands elsewhere in the East China Sea.

China claims the string of islands – which Japan refers to as the Senkakus and are known as the Diaoyu by Beijing – as its own, and regularly sends ships and aircraft into the area to test Tokyo’s response times.

China also has disputes with several other nations in the South China Sea, which it claims in its entirety.

AloJapan.com