Retailers have told food safety chiefs they are removing beef products from their shelves after tests uncovered traces of horse meat in burgers.
A study by the Food Safety Authority of Ireland (FSAI) said beef burger products which tested positive for horse DNA were produced by two processing plants in Ireland and one plant in the UK. They were on sale in Tesco, Dunnes Stores, Lidl, Aldi and Iceland.
Professor Alan Reilly, chief executive of the FSAI, said while these findings do not pose a public health risk they do raise some concerns.
"The products we have identified as containing horse DNA and/or pig DNA do not pose any food safety risk and consumers should not be worried. Consumers who have purchased any of the implicated products can return them to their retailer," he said.
According to the research by the FSAI, one sample of burger goods, Tesco Everyday Value Beef Burgers, showed about 29 per cent horse meat relative to beef content.
"Whilst there is a plausible explanation for the presence of pig DNA in these products due to the fact that meat from different animals is processed in the same meat plants, there is no clear explanation at this time for the presence of horse DNA in products emanating from meat plants that do not use horse meat in their production process," Prof Reilly said.
"In Ireland, it is not in our culture to eat horse meat and therefore, we do not expect to find it in a burger."
Tesco said they are working with the authorities in Ireland and the UK, and with the supplier, to urgently understand how this has happened and "to ensure it does not happen again."
A spokesman said: "We will not take any stock from this site until the conclusion and satisfactory resolution of an investigation."
Aldi said they were conducting their own investigation.
"We have sought information from one supplier, Silvercrest, which is dealing directly with the FSAI on the issue that has been raised," the company said.
Lidl has removed all implicated products from sale pending a full investigation.
"A refund will be provided to customers who wish to return affected products," said a spokesman