Tesco has placed full-page adverts in newspapers apologising to customers for selling beef burgers containing horse meat.
It has also promised to refund customers who bought the contaminated products, and said sorry for the "unacceptable" situation.
The apology came as a food expert claimed horse meat could have been in beef burgers for years, but remained undetected because of insufficient food regulation.
The UK's food watchdog, the Food Standards Agency (FSA), is also considering taking legal action against companies at the centre of the scandal.
Tesco promised refunds to customers who had bought the contaminated products, which it identified as Tesco Everyday Value 8 x Frozen Beef Burgers (397g), Tesco 4 x Frozen Beef Quarter Pounders (454g), and a branded product, Flamehouse Frozen Chargrilled Quarter Pounders.
In the advertisement, entitled "We apologise", Tesco says: "While the FSAI ( Food Safety Authority of Ireland) has said that the products pose no risk to public health, we appreciate that, like us, our customers will find this absolutely unacceptable."
It continues: "We have immediately withdrawn from sale all products from the supplier in question, from all our stores and online... We and our supplier have let you down and we apologise."
The advert concludes: "So here's our promise. We will find out exactly what happened and, when we do, we'll come back and tell you.
"And we will work harder than ever with all our suppliers to make sure this never happens again."
The apology came as a reported €360m million was wiped off Tesco's stock market value.
The FSA said it would consult relevant local authorities and the Food Safety Authority of Ireland (FSAI) over whether to take action against any organisations embroiled in the controversy.
But the organisation was criticised for not carrying out tests in the past because horse meat posed no threat to public health.