A U.S. livestock industry group said Friday it opposes a government plan to ease a four-year import ban on Japanese beef because of mad cow disease unless Japan simultaneously lifts its ban on American beef.

The National Cattlemen's Beef Association said it "will not support finalization of this proposed rule until Japan has completed its process and accepts beef from the U.S.

"The United States has repeatedly called on Japan to open the border to U.S. beef, and NCBA calls for this action simultaneously to allowing imports of Japanese beef into the United States," it said.

The U.S. banned Japanese beef imports in September 2001 following the discovery of the first case of mad cow disease, or bovine spongiform encephalopathy, in Japan.

The U.S. Department of Agriculture on Tuesday proposed easing the ban under certain conditions, including completely removing specified risk materials, such as spinal cords and brains, from carcasses. The USDA will receive public comments on the proposal until Sept. 19.

Japan imposed its import ban on American beef in December 2003 when the U.S. discovered its first mad cow case.

The two countries agreed in principle in October that Japan would resume imports of American beef from animals aged up to 20 months.

But it is taking time for Japan to ease the ban due to domestic procedures, including a go-ahead from an expert panel, and this is irritating the United States.

Japan conducts blanket testing for mad cow disease on all animals aged 20 months or older, while the United States only tests a small percentage of animals.