Britain's food regulator said on Friday that testing had found horsemeat in ground beef at Taco Bell UK fast-food outlets, a discovery that puts new pressure on parent Yum Brands Inc, which is grappling with a food safety scare in China.
Taco Bell said the horsemeat issue is isolated to its UK market, where the Mexican-inspired chain has just three restaurants, and that it will step up testing of its beef.
On Monday, Yum said it would stop using more than 1,000 poultry slaughterhouses in China as it moves to tighten food safety and reverse a sharp drop in business at KFC restaurants in its top market after a scare over contaminated chicken.
Europe's horsemeat scandal erupted in January, when testing in Ireland revealed that some beef products also contained equine DNA.
It since has spread across the continent, ensnaring numerous well-known brands, prompting product withdrawals, consumer concerns and government investigations into the region's complex food-processing chains.
Britain's Food Standards Agency (FSA) said on Friday it had conducted 1,797 tests over the last seven days. More than 99 percent of the readings came back negative for horsemeat levels at or above 1 percent.
However, four tests were positive, it said. They were for Taco Bell ground beef, beef skewers made by catering company Brakes, and two types of Birds Eye ready meals - spaghetti bolognese and beef lasagne.
The Birds Eye meals were withdrawn from sale last week after tests on a product the company sold in Belgium produced by the same supplier came back positive.
The FSA said no tests to date on samples containing horse DNA had found the veterinary medicine phenylbutazone (bute), which is banned from most medical uses in humans for safety reasons.
Taco Bell tested the meat at its UK restaurants as soon as news of the horsemeat contamination surfaced, Taco Bell UK spokesman Christopher Fuller said in a statement.
"Based on that testing we learned ingredients supplied to us from one supplier in Europe tested positive for horsemeat. We immediately withdrew it from sale, discontinued purchase of that meat and contacted the FSA with this information," Fuller said.
Taco Bell, like many other companies, cannot say for certain whether any of the horsemeat-tainted product was served to consumers, Fuller said.
The chain will test every batch of ground beef when it arrives at its processor and again before it is delivered to restaurants to make sure it is 100 percent beef, Fuller said.
"We apologize to our customers and take this matter very seriously," he added.
Yum has seen a sharp drop in business at its nearly 5,300, mostly KFC, restaurants in China after news reports and government investigations in the Asian country focused on chemical residue found in a small portion of its chicken supply.
Yum was not fined by Chinese food safety authorities.
Hamburger chain Burger King in January said traces of horse DNA had been found in samples of hamburger patties from a food-processing plant in Ireland but that the meat never reached its restaurants.
Shares in Yum were off 0.6 percent at $65.07 in midday trading on the New York Stock Exchange.
Earlier on Friday, the British Retail Consortium, an industry body, said the latest round of testing by grocers including all the major supermarkets had produced no new positive results.