Liberal Democratic Party Secretary General Tsutomu Takebe criticized Beijing on Sunday over a news report that Chinese maritime authorities have banned ship traffic in the East China Sea near the median line with Japan while it expands the Pinghu gas field.

According to Japanese Embassy sources in Beijing, the area straddles the disputed median line between the two countries and extends into waters Japan considers its exclusive domain.

During a Fuji TV program Sunday morning, Takebe expressed "regret" over the reported Chinese move, saying Tokyo would lodge a formal protest if the report is confirmed.

The embassy sources said the Japanese government was inquiring with the Chinese side to confirm the facts of the situation.

NHK quoted Foreign Minister Taro Aso as saying Sunday he had not heard of the Chinese move and could not comment.

Japan regards the median line as separating the two countries' 200-nautical-mile exclusive economic zones.

The purpose of the expansion work, to last until Sept. 30, is to lay pipelines and cables on the seabed, according to the Web site.

Apart from the Pinghu field, China has said the Chunxiao field, a gas field which lies south of Pinghu and is under Chinese development, will begin commercial operation within the first half of this year.

Japan fears that Chinese development of the gas fields will siphon off resources on the Japanese side of the median line. Although the government granted drilling rights to Teikoku Oil Co. last year, it has yet to start drilling out of security concerns.

China's explosive economic growth of nearly 10 percent per year since 1995 has fed its demand for resources.