Japanese officials have told a visiting U.S. delegation that it is "too early" to reopen the door to American beef imports, and indications are that the ban imposed last week might not be lifted for some time.

Japan says it will send a delegation to the United States next month to investigate the safety of U.S. beef.

That was the only progress reported after a team led by a trade adviser to the U.S. agriculture secretary met Monday with senior officials of Japan's agriculture, health and foreign ministries.

The Japanese rejected a request by the delegation to lift the ban on U.S. beef, which was imposed last week after the discovery of a case of mad cow disease in Washington State.

The United States contends there are no valid health reasons for a total prohibition, since certain cuts of meat carry no danger of bovine spongiform encephalopathy, or BSE, the clinical name for the disease.

Industry officials say the best the United States can hope for is that Tokyo will allow the entry of tens of thousands of tons of chilled and frozen beef already en route to Japan.

Japan is the biggest importer of U.S. beef, buying more than $1 billion worth each year. But Japanese officials say that before they will lift the ban, they want Washington to put into place a comprehensive testing program. That could take a considerable length of time.

Japan itself is no stranger to the brain-wasting disease. It has reported nine confirmed cases of mad cow in its own herds in the past two years, since it put into place one of the world's strictest testing programs.

Scientists say the only way for humans to contract the disease is by eating neural tissue of cows infected with BSE. However, the World Organization for Animal Health recommends that countries shut down beef trade with any nation that has reported a mad cow case.

The leader of the American delegation, David Hegwood, has had previous success in negotiations with the Japanese. In May, he helped prevent a prolonged cutoff of U.S. beef exports to Japan after a cow tested positive for BSE in Alberta, Canada.

Japan, which has barred Canadian beef, at the time said it was concerned about the U.S. supply as well, because of extensive cross-border cattle trading in North America.

A preliminary investigation has indicated that the infected Holstein in Washington State probably came into the country from Canada.

The U.S. delegation is also expected to visit South Korea, the second-biggest importer of U.S. beef and one of more than 20 countries that have halted American beef imports. That amounts to about 90 percent of U.S. cattle ranchers' export market.