"I can't comment at this point on the matter as I don't know the details of the lawsuit," Toyota Motor Corp chairman Fujio Cho said at a regular news conference of the Japan Automobile Manufactures Association, which he chairs.

California on Wednesday announced that it has filed a civil suit against six automakers: Chrysler, General Motors and Ford and the North American units of Japan's Toyota, Honda and Nissan.

Nissan Motor Co and Honda Motor Co also said they could not comment on the lawsuit.

The suit is the first of its kind in the United States seeking to hold manufacturers liable for damages allegedly caused by greenhouse gases produced by their vehicles.

Japanese automakers have in recent years cashed in on an eco-friendly reputation, with their hybrid cars that use less gasoline a major hit in North America.

California, led by Republican actor-turned-Governor Arnold Schwarzenegger, has broken with US President George W. Bush on environmental issues.

Schwarzenegger has backed legislation to reduce greenhouse gas emissions making California the first US state to commit to adhering to the Kyoto Protocol.

The United States and Australia are the industrialized world's two major holdouts from the Kyoto Protocol, the landmark environmental treaty reached in Japan's ancient capital.

Toyota and Nissan, along with five other Japanese automakers, earlier faced a lawsuit in Tokyo by asthma patients who said their illness was caused by hazardous diesel fumes.

In October 2002, the Tokyo District Court punished Japan's central and Tokyo governments in the suit, but did not question the responsibility of carmakers.