Aldi has suspended its contract with beefburger supplier Dalepak after DNA tests found small traces of horsemeat in its products.
The supermarket withdrew three beefburger lines earlier this month after traces of pig meat and horsemeat were discovered, and launched an investigation.
"Aldi UK's customers are our absolute priority," a spokesman said. "This is why we immediately withdrew these products until such a time that we could verify that there was no risk to our customers.
"We are deeply angry and feel let down by our supplier and we are pursuing more tests until we are certain that we understand how the production line was contaminated."
Three random samples of each Aldi's UK beefburger products, all from different batches, were tested for traces of non-beef animal DNA.
For each product, two of the three samples came back negative - that is, they had no trace of DNA other than beef.
However, on one of each of the samples, the tests revealed a 0.1% trace of non-beef DNA.
Specially Selected Aberdeen Angus Quarter Pounder contained 0.1% pork, Oakhurst Beef Quarter Pounders had 0.1% pork and 0.1% equine, while Frozen Oakhurst Beefburgers tested positive for 0.1% equine.
Aldi's statement added: "While these traces are at the lowest forensically detectable level through DNA-testing, they do corroborate Aldi UK's decision to remove these products from sale. We can confirm that there is no risk to food safety emerging from the findings."
The supermarket giant's technical director Tim Smith said: "The evidence tells us that our frozen burger supplier, Silvercrest, used meat in our products that did not come from the list of approved suppliers we gave them."
Earlier this week Irish food and agriculture officials said horse meat found in burgers came from a Polish supplier, who sent Silvercrest frozen blocks of slaughterhouse leftovers that were labelled as beef.
But a Polish official said he has seen no evidence to support the claim.
Burger King has also dropped Silvercrest, but says none of its horsemeat-contaminated products were sold in its stores.
In a statement it said: "Within the last 36 hours, we have established that Silvercrest used a small percentage of beef imported from a non-approved supplier in Poland.
"They promised to deliver 100% British & Irish beef patties and have not done so. This is a clear violation of our specifications, and we have terminated our relationship with them."