Japan said Monday that it is too soon to discuss lifting its ban on American beef, saying that officials should first establish the facts surrounding the discovery of a case of mad cow disease (search) in the United States.

Agriculture Ministry officials spoke after talks with a U.S. delegation that came to Tokyo to discuss the discovery of the disease in a Holstein in Washington State that has prompted more than two dozen countries to ban American beef imports.

Japan is the largest overseas market for U.S. beef, importing more than $1 billion worth last year.

The U.S. delegation asked to discuss lifting the ban, a Japanese official said on condition of anonymity.

"First we have to confirm the facts, so it's too early to have such a discussion," the official said.

A U.S. official, who also spoke on condition of anonymity, said the meeting was intended primarily to brief Japanese authorities on efforts in the United States to investigate the case and to investigate the route of infection, which has been tentatively traced to Canada.

Japanese agriculture officials said the delegation, which was led by a trade adviser to U.S. Agriculture Secretary Ann Veneman, assured them that the United States would soon announce more stringent safety measures.

Dr. Ron DeHaven, the U.S. Department of Agriculture's (search) chief veterinarian, said Sunday that trade restrictions "are not well-founded in science" because research shows that certain meats, such as beef steaks and roast, are safe from infection.

Japan suffered an outbreak of mad cow disease two years ago, prompting authorities to adopt a system under which all cattle bound for slaughter in the country are tested for the disease formally known as bovine spongiform encephalopathy, or BSE.