The Co-operative Group says tests of its own-brand burgers, supplied by Silvercrest, found traces of less than 1% horse DNA in three samples and 17.7% in one sample.
Our decision to withdraw these products at the first opportunity and cease taking further product from this site has proven to be the correct course of action.
Whilst there are no safety issues involved, it is now apparent that some of the withdrawn products have not met the high standards we and our customers expect. We apologise for this.
We specify that all meat in our frozen burgers should be 100% British but we now strongly believe that some of the meat used to produce these burgers came from outside the UK and was not British in origin, and as a result we have taken the decision to delist Silvercrest as a supplier with immediate effect.
In addition we are tightening our already stringent quality checks to ensure our products meet the high specifications that we set on behalf of our customers.
Iceland's Technical Manager Trish Twohig told the Commons Environment Committee that the supermarket was "passionate about food safety" and that future product assessments would "include equine testing".
The food processing group which owns the Irish supplier Silvercrest - dropped by Tesco after an investigation into how horse DNA ended up in its frozen burgers - says it has introduced new measures to audit where its meat comes from.
Tesco has promised customers that introducing DNA checks "will set a new standard" in the testing of meat products.
The supermarket said that the discovery of horse DNA in frozen burgers shows that "in spite of our stringent tests, checks and controls, there remained a small possibility that something could go wrong and it did."
"We want to stop it ever happening again, so we are taking action to reduce that possibility still further."
The Food Safety Authority of Ireland (FSAI) found horse DNA earlier this month in beef burger products sold by Tesco and several other supermarkets.
It said most of the affected burgers contained very low levels of horse DNA, but in one Tesco sample horse meat accounted for about 29 percent relative to the beef content.
Tesco says it will now introduce a "comprehensive system of DNA testing across our meat products."
The supermarket giant says it's taking action to show its customers that they can trust the quality of its food.
"We want to leave customers in no doubt that we will do whatever it takes to ensure the quality of their food and that the food they buy is exactly what the label says it is", Tesco's Technical Director Tim Smith said.