LONDON - British Prime Minister David Cameron voiced concern Wednesday about the "extremely disturbing" discovery of horsemeat in beefburgers sold in supermarket giants.
The Food Safety Authority of Ireland (FSAI) revealed Tuesday that up to 29 percent of the meat content of some beefburgers was in fact horse, while they also found pig DNA.
The frozen burgers were on sale in high-street supermarket chains Tesco and Iceland in both Britain and Ireland, and in Irish branches of Lidl, Aldi and Dunnes Stores. Tesco is Britain's biggest retailer.
The FSAI said the burgers had been made at two processing plants in Ireland and one in northern England.
Simon Coveney, Ireland's agriculture and food minister, said the source of the problem appeared to be products imported from the Netherlands and Spain.
While horsemeat is a common sight in central Asia, China, Latin America and parts of Europe, it is considered taboo by most British and Irish consumers.
Out of 27 products the FSAI tested, 10 were found to contain horse DNA and 23 had pig DNA.
In nine of the 10 with equine DNA, horse accounted for 0.3 percent or less of the meat content.
However, it made up 29.1 percent of the meat content in Tesco's low-end Everyday Value Beef Burgers.
Cameron told parliament in London that it was an "extremely serious issue".
"People in our country would have been very concerned to read this morning that when they thought they were buying beefburgers, they were buying something that had horsemeat in it," he said.
"That is extremely disturbing news.
"I've asked the Food Standards Agency to conduct an urgent investigation into this. They have made clear that there's no risk to public safety because there's no food safety risk but this is a completely unacceptable state of affairs."
He said the FSA would be meeting with retailers and processers to investigate the supply chain, but stressed that "ultimately retailers have to be responsible for what they sell and where it has come from".
Tim Smith, Tesco's group technical director, said the company "immediately withdrew from sale all products from the supplier in question".
"We will not tolerate any compromise in the quality of the food we sell," he added.
Iceland said they were taking two products off the shelves as a "precautionary measure".