Japan has asked China to explain reports that the Chinese have banned ships from entering a disputed area of the East China Sea while they lay a pipeline and cables under the sea. The Chinese have yet to answer Japan's query.

A spokesman for the Japanese Embassy in Beijing, Ide Keiji, tells VOA his government is seeking more information from China before it decides whether to lodge a formal protest.

"We are not so sure of what the Chinese side is really doing in that area, or what is their plan. So, first we want to know details of the Chinese plan," he said.

In Tokyo, Chief Cabinet Secretary Shinzo Abe said Japan has expressed his concern about the report, which, if true, may violate international maritime law. Japan says the notice announcing the ban appeared on an official Chinese maritime website.

Japanese officials say the warnings were published last month, but it was not until last week that Tokyo first raised the issue with the Chinese authorities.

Chinese Foreign Ministry officials on Monday had no comment on Japan's statements. Japan says Beijing has promised to look into the matter and respond.

Japan and China have been locked in a dispute over rights to a gas field in the East China Sea, between the two countries. Several rounds of negotiations recently have failed to make any progress.

Japan claims it has rights up to a middle point of the disputed area, while China claims a wider section that contains the entire field.

Relations between China and Japan have been strained in the last few years - largely due to Beijing's stepped-up criticism over what it says is Japan's failure to face up to atrocities committed by Japanese troops during their occupation of China in the first half of the 20th century.

Japanese Prime Minister Junichiro Koizumi has angered China for paying annual visits to a shrine near Tokyo where convicted World War II criminals are among those honored.

Japan's query over access to the East China Sea lanes comes a few days before Chinese President Hu Jintao visits the White House.