A Japanese government food safety panel expressed concern Saturday about a second confirmed U.S. mad cow case, raising speculation that Tokyo (search) may delay a resumption of American beef imports.

Taiwan (search), meanwhile, reimposed the ban on U.S. beef that it had lifted just two months ago.

Japan was the United States' largest overseas market for beef before Tokyo banned all American beef imports 17 months ago following the first confirmed U.S. mad cow case. Japan (search) imported more than $1.5 billion worth of U.S. beef in 2003 before it imposed the ban, the U.S. Department of Agriculture said.

Washington has recently intensified pressure on Tokyo to resume beef imports, with some officials threatening sanctions.

Two months ago, Taiwan lifted the ban it had imposed in February 2004. Chen Lu-hung of the Heath Department's Food Control Section said Saturday the renewed ban would take effect immediately.

In the year before the ban, Taiwan imported more than $76 million in U.S. beef and beef products, according to the USDA.

When results in the latest U.S. case were still pending several days ago, Japanese officials said it was unlikely to delay negotiations with Washington on restarting imports of American beef.

But Friday's confirmation of the case raises the need to examine the accuracy of U.S. testing and the extent of the illness there, Food Safety Commission member Kiyotoshi Kaneko said.

"There is a big difference between a suspected case and a confirmation," Kaneko said in an interview aired by public broadcaster NHK.

Japan's Agriculture Ministry plans to ask Washington to provide more information about the affected cow, including details about its origin and feed, NHK said.

Japanese consumer groups on Saturday renewed their demand that the government keep the ban in place.

"If any doubts remain, we cannot buy American beef if it returns to our market," Toshiko Kanda, head of Consumers Japan, told NHK.

It is believed that eating meat from animals with mad cow disease, also called bovine spongiform encephalopathy or BSE, can cause humans to contract variant Creutzfeldt-Jakob disease — a fatal brain-wasting disorder that has killed more than 150 people, mostly in Britain in the 1990s.

Canadian officials have expressed hope that the latest disease finding will lead to the quick reopening the American border to cattle from Canada, where ranchers have been devastated by a ban that has cost the industry $5.6 billion.

"There is really no excuse to delay opening up the border. It has to be open. The American administration is behind us. Canadian science clearly shows this and it should open now," Prime Minister Paul Martin said from Alberta, a province hit hard by the ban.

The USDA only recently has tried to lift the U.S. ban imposed after the first of three Canadian BSE cases appeared in 2003. The border was scheduled to reopen in March, but a federal judge in Billings, Mont., ordered it kept closed at the request of ranchers suing to block Canadian cattle imports.

Hearings on the ban are scheduled for July.

Canadian ranchers have called it protectionism.