Birds Eye has named an Irish meat processor as the source of horse meat found in its lasagne and spaghetti bolognese.
The frozen food giant said one of its suppliers had itself been supplied by QK Meats, which it has now suspended.
Birds Eye took its Spaghetti Bolognese 340g and Beef Lasagne 400g off shelves as a precaution on February 22 but tests later found that they did contain some horse DNA.
In a statement, the company said: "As you know, we unfortunately had to withdraw a small number of our overall beef product range from sale on the February 22.
"We told you how sorry we were for letting you down and that we would keep you informed of what action we were taking and, once we got to the bottom of the problem, tell you how it happened.
"We can now reassure you that our comprehensive DNA testing programme on all our beef meat products is complete. We have now tested all products multiple times through multiple samples over a period of four weeks.
"During this process none of our Birds Eye Beef Burgers, Beef Pies and Traditional Beef Dinners tested positive for horse DNA."
It added: "We are pleased that we have now completed our investigation and been able to isolate the problem to one source."
The statement said Birds Eye had introduced a "triple lock" programme to ensure that no minced beef meat product can reach supermarket shelves without first having been cleared by three stages of DNA testing.
"We feel the same as our customers do - this should never have happened, but now that it has, it is up to us to make sure we do all we can to avoid it happening again."
Responding to Birds Eye's claims, QK Meats said: "The quality and safety of our products is of the utmost importance to QK Meats," a company spokesman said.
"The company has been operating for the past 25 years and has an exemplary record in terms of food quality and safety standards. QK Meats has never knowingly incorporated horsemeat into any of its beef products."