Fast food chain Burger King said traces of horse DNA were found in samples of patties from a food-processing plant in Ireland but that the meat never reached its eateries.
"Four samples recently taken from the Silvercrest plant have shown the presence of very small trace levels of equine DNA. This product was never sold to our restaurants," the company said in a statement on Thursday.
"They promised to deliver 100 percent British and Irish beef patties and have not done so."
Burger King previously dropped the firm, which had been approved to supply burgers to its restaurants in Britain, Ireland and Denmark.
Traces of horse DNA were found in beef burgers sold by supermarkets Tesco, Lidl, Aldi and Iceland .
"We are deeply troubled by the findings of our investigation and apologise to our guests, who trust us to source only the highest quality 100 percent beef burgers. Our supplier has failed us and in turn we have failed you." said Burger King's vice president of global quality, Diego Beamonte.
The Miami-based chain said its investigation showed the source of the Silvercrest contamination was the same non-approved Polish supplier identified by the Irish department of agriculture.
Food safety experts said horse meat poses no added health risks to consumers, but the discovery has raised concerns about the food supply chain and the ability to trace meat ingredients.