Japan has announced it is reimposing a ban on all U.S. beef products. Government officials say they were forced to make that decision after spinal material considered risky for bovine spongiform encephalopathy - also known as mad cow disease - was discovered in an incoming shipment from the United States.

Japan made a quick decision Friday, just hours after announcing the discovery of suspect material in imported American meat, to reinstate a ban on U.S. beef.

Japanese Prime Minister Junichiro Koizumi says he has endorsed a proposal from the agriculture minister, Shoichi Nakagawa, to totally halt American beef imports.

The prime minister says ensuring food safety is extremely important and that he told Nakagawa it was a good idea to accept the recommendation to ban U.S. beef imports.

Nakagawa has called the incident a serious violation of the import process.

A two-year ban on U.S. beef was conditionally lifted last month. The agreement between Tokyo and Washington stipulated no meat would be sent to Japan from cattle over the age of 20 months, and spinal cords and other specified risk material that could transmit mad cow disease would be removed.

U.S. Embassy spokesman Michael Boyle in Tokyo says the American government will conduct a full investigation.

"We look forward to knowing the results of that investigation," said Boyle. "The United States has every intention of living up to the letter of our recent agreement in regard to beef imports into Japan and we will work closely with the appropriate authorities here in Japan and in the United States to ensure there is no repetition of this mistake."

Japanese officials say the suspect spinal material was found in a 390-kilogram shipment from New York at Narita airport, outside Tokyo. The beef had been imported by a Japanese trading company as a sample product.

Before the initial ban in December 2003, Japan was the top foreign buyer of U.S. beef - with the imports totaling $1.4 billion annually.