According to Japanese officials, China violated an agreement it had brokered with Japan in 2008 to jointly develop gas fields in the East China Sea. From Reuters:
Foreign Minister Hirofumi Nakasone said China had been drilling in violation of a June 2008 agreement with Japan and that Tokyo had protested as soon as it became aware. He did not specify when this happened.
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“Under last June’s agreement, we were meant to continue negotiations about the areas on which there was no political consensus. So this is most regrettable and we are protesting to the Chinese government,” Nakasone told reporters.
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The Chinese foreign ministry said in a statement on its website at the weekend that developing the field was an “inherent sovereign right of China”.