Japan threatens action on China gas project - report
Although the two countries reached a broad agreement in 2008 on principles intended to solve the dispute by jointly developing gas fields, progress has been slow and Japan has accused China of drilling for gas in violation of the agreement.
A Japanese Foreign Ministry official said Foreign Minister Katsuya Okada told his Chinese counterpart Yang Jiechi at a meeting in Tokyo on Sunday of certain counter-action, but did not elaborate, Kyodo reported.
Tokyo objects to Chinese development of the Chunxiao gas field in seas close to Japan's claimed boundary.
Estimated net known reserves in the disputed fields are a modest 92 million barrels of oil equivalent, but both countries have pursued the issue because there may be larger hidden reserves.
(Reporting by Hideyuki Sano; Editing by Jeremy Laurence)