In what may be the first case of mad cow disease in the United States ever, agriculture officials announced Tuesday a suspected case of the disease has been found in Washington state.

Japan and South Korea have both temporarily suspended imports of U.S. beef -- Canada will wait until the suspected case is confirmed before taking any possible action.

Official results are expected late Christmas Day.

U.S. Agriculture Secretary Ann Veneman told a press conference mad cow is suspected in a single animal and her department was taking "all appropriate action" to deal with the case.

"Despite this finding we remain confident in the safety of our food supply," Veneman said.

The farm near Yakima, Wash., where the cow originated, has been quarantined and officials are scrambling to figure out what happened to beef from the infected animal. They admit they are not positive where it went.

But, Veneman said the single cow that initial tests showed may have the brain-wasting illness was either sick or injured and was never destined for the U.S. food supply.

A tissue sample from the animal was tested on Dec. 9 as part of a continuing government program -- it proved "presumptively positive" for mad cow disease.

More tissue samples from the animal were being sent to a British animal laboratory to confirm the initial U.S. tests.

"That will take probably 3 to 5 days to get final results from that sample," Veneman said.

On May 20, Canada confirmed its first and only case of mad cow disease, also known as bovine spongiform encephalopathy (BSE).

The discovery of BSE in a single Alberta cow led the U.S. and numerous other countries to shut their borders to Canadian beef.

Japan and South Korea took immediate action to halt imports of U.S. beef with the announcement of the U.S. case.

Japan's Agriculture Ministry said the country was indefinitely banning beef imports. Japan is the largest overseas market for U.S. beef. Exports totalled $842 million US in 2002, the U.S. Meat Export Federation said.

The South Korean government also halted customs inspection of U.S. beef, a move that effectively keeps it from reaching the domestic market.

Meanwhile, the Canadian Food Inspection Agency said it has no immediate plans to close Canada's border to beef from U.S.

Dr. Brian Evans, chief veterinary officer, told an Ottawa press conference federal officials would wait for confirmation the cow identified in Washington had mad cow before making any decision on U.S. beef imports.

"It's appropriate we all take a measured response but that we take it based on all known facts," Evans said.

Earlier, Veneman told reporters it was unlikely there was a connection between the Alberta case and the suspected Washington case.

"It is way to early to tell but I would think the situation of trying to put those two incidents together would be doubtful, primarily because they are different kinds of animals. This was a Holstein cow," she said.

A Holstein cow is typically used in the production of dairy products, while the Alberta cow was a beef cow.

Rookie Canadian Agriculture Minister Robert Speller was expected to comment in what will be his first major test since taking office less than two weeks ago.

Import bans on Canadian beef halted sales to 34 markets, dealing a devastating blow to the industry. It cost exporters alone more than $1.9 billion.

The U.S. partially lifted its ban in September to allow imports of some boneless cuts of beef from young animals, which are not considered susceptible to BSE.

Since then, more than 60,000 tonnes of beef has moved into the United States and Mexico.

Mad cow disease first sprang up in Britain in 1986 and spread through countries in Europe and Asia, prompting massive destruction of herds and decimating the European beef industry.

Scientists believe the deadly human form of mad cow disease, known as variant Creutzfeldt-Jakob disease, comes from eating products from cows infected with BSE.