As China acknowledged that it had moved a new squadron of warships into the East China Sea, it also sent negotiators to Tokyo to resume talks about the massive undersea energy field straddling the border of their exclusive economic zones.
Japan estimates the disputed field holds at least 200 billion cubic meters of gas. China started test drilling in the region two years ago. Japan took action of its own in July, by granting permission for a Japanese entity to prepare for exploration.
Those moves followed decades of restraint by the two Asian nations. But increasingly, the two, both huge importers of oil and gas, are competing to fill their energy appetites.
The dispute literally flared up earlier this month when Japan said it had spotted flames shooting from a drilling platform in the area. The platform was just inside what Japan calls the Chinese side of the dividing line, suggesting that China was involved in major drilling activity.
Japanese Foreign Ministry deputy press secretary Tomohiko Taniguchi on Friday told reporters the Tokyo meeting signals a good start, in the sense that the two nations are talking face-to-face. But he also reiterated Japan's stance, that China should immediately halt any oil or gas extraction it may be conducting.
"If anything is done from the Chinese side, unilaterally, it has to be stopped, and we have to talk with each other and to exchange information - information as to what sort of scientific evidence is there, as to existence and places of resources," said Tomohiko Taniguchi.
Japan's NHK network reported Friday evening, without attribution, that in response to Tokyo's expressions of "strong concern," the Chinese negotiators said their development is taking place in Chinese waters, and should cause no problem for the Japanese.
Japan says any exploitation on the Chinese side could be sucking resources from across the maritime demarcation line. Tokyo is offering a compromise of joint exploration, but China, which has long disputed Japan's definition of the boundary, has so far rejected the offer.
China's state-run media say a reserve flotilla of naval warships recently dispatched into the area is meant to fight wars and handle peacetime emergencies, as well as to eliminate what it calls "obstacles at sea."
The talks are set to conclude on Saturday.