Tokyo Gov. Shintaro Ishihara warned Friday the Tokyo Metropolitan Government may sue the central government unless it acts on his demands for tougher regulations governing diesel vehicle emissions.

Earlier in the day, the metropolitan government submitted a letter to Prime Minister Junichiro Koizumi questioning the awareness of the central government regarding air pollution caused by these vehicles. The same letter was sent to Environment Minister Shunichi Suzuki.

Ishihara has accused Koizumi of failing to live up to his repeated promises to adopt the world’s toughest regulations on diesel vehicle exhausts.

“I can’t help saying that (the central government has been) deceptive. If we cannot receive a sincere response, we intend to sue,” Ishihara told a news conference.

In the letter, Ishihara stated that Japan should adopt tougher regulations on particulate matter emitted by new diesel vehicles than those scheduled to be implemented by the United States.

Beginning in 2007, the U.S. will stipulate particulate matter emissions of 0.013 grams per kwh for new diesel vehicles that weigh 3.5 tons or more. Beginning in 2005, Japan plans to enforce 0.027 g/kwh for the same category of vehicles.

The metropolitan government has also urged the central government to take prompt action to promote the use of diesel oil featuring a sulfur content of 10 parts per million or lower. This type of fuel is set to become available in Japan in 2005.

In October, the metropolitan government will enforce new regulations governing the diesel vehicle emissions of buses and trucks. Diesel vehicles that fail to meet the new regulations will be banned from use in Tokyo or will need to be equipped with special features that reduce emissions of particulate matter.