Japan has conveyed "serious concerns" to Beijing over moves by its vessels around one of a string of disputed gas fields in the East China Sea, wary that China may be seeking to tap the field on its own, Foreign Minister Hirofumi Nakasone said Tuesday.
"We have called on China not to take actions that will undermine confidence," Nakasone said, adding the Chinese vessels may by carrying materials for future development of the Chinese-operated Chunxiao gas field, known as Shirakaba in Japan.
"We have not confirmed drilling equipment, but if there are other materials that are for preparations for future development, this would be a big problem," he said.
China has said the move is for "maintenance and management" of the gas field, according to Nakasone.
As part of an agreement reached in June 2008 over gas exploration projects in the East China Sea, China welcomed investment by Japanese corporations in the project at the Chunxiao gas field.
But more than a year has passed without the two countries starting negotiations toward concluding a treaty to implement the agreement. Japan says development should be suspended until the treaty is concluded.