Countries across Asia have temporarily halted imports of US beef after that country's first suspected case of "mad cow disease" was announced.
Japan, South Korea and Singapore acted within hours of the news that a cow had tested positive in Washington state.
Japan is the largest buyer of US beef, and has had its own BSE scare with nine cases of the disease.
Australia, the world's largest beef exporter, saw meat prices rise sharply in anticipation of extra sales.
Japan and South Korea are major importers of US beef
South Korea's agricultural ministry said it would suspend customs procedures on all US beef - effectively ending imports.
An agricultural ministry official told Yonhap, the state news agency, that this was just a temporary measure and the final decision to ban US beef would be made only after official test results were announced.
About two-thirds of beef imported to South Korea is from the United States.
Analysts have said that if the ban continues, the country would have to rely more on countries like Australia for its main source of imports.
Japan's agricultural ministry also announced a temporary ban on US beef imports.
According to the US Meat Export Federation, last year Japan bought more than $800m million dollars of American beef, accounting for about 30% of the total value of US exports of the meat.
Hong Kong and Taiwan also suspended US beef imports.
Eating BSE-infected beef has been linked to a new variant of the brain-wasting condition Creutzfeldt-Jakob Disease (vCJD), which has killed more than 130 people in Britain since 1996.