Investigations are under way to try to find out how beefburgers on sale in UK and Irish Republic supermarkets became contaminated with horsemeat.
Irish food safety officials, who carried out tests two months ago, said the products had been stocked by a number of chains including Tesco and Iceland stores in the UK.
They said there was no human health risk and the burgers had been removed.
Tesco said it was "working... to ensure it does not happen again".
The UK's Department for Environment, Food and Rural Affairs (Defra) said it was working with the Food Standards Agency (FSA) to "urgently investigate" how the products came to contain horsemeat.
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The investigation will trace the meat back to its source to "find the cause of the contamination". The FSA has also called a meeting of food industry representatives.

The Food Safety Authority of Ireland (FSAI), which is conducting similar inquiries, said the meat had come from two processing plants in the Irish Republic - Liffey Meats and Silvercrest Foods - and the Dalepak Hambleton plant in North Yorkshire.


The burgers had been on sale in Tesco and Iceland in the UK and the Republic of Ireland, where they were also on sale in Dunnes Stores, Lidl and Aldi.
A total of 27 burger products were analysed, with 10 of them containing traces of horse DNA and 23 containing pig DNA.
'Extremely serious'

Horsemeat accounted for approximately 29% of the meat content in one sample from Tesco, which had two frozen beefburger products sold in both the UK and Ireland contaminated with horse DNA.
In addition, 31 beef meal products, including cottage pie, beef curry pie and lasagne, were analysed, of which 21 tested positive for pig DNA.
FSAI director of consumer protection Raymond Ellard said several investigations would now need to take place.He said: "The companies have taken a very responsible attitude. On a voluntary basis they have withdrawn products from sale, so have the retailers.