The Department of Agriculture has said that preliminary laboratory results indicate the presence of horse DNA in nine out of 13 samples of finished burgers at the Silvercrest plant.

The burgers were manufactured between 3 and 14 January.

The samples were taken by the Department of Agriculture on Tuesday 15 January.

Of the seven samples of raw ingredients tested, one was positive and came from another EU member state.

All ingredients in the production of the burgers sourced from Irish suppliers were negative.

Further tests are being carried out in Germany.

ABP Food Group, which owns Silvercrest, have said that it has suspended all production with immediate effect.

Tests from Liffey Meats have not yet been completed.

It is hoped that the results may go some way towards explaining how horse meat and traces of pig ended up in burgers for sale in supermarkets around Ireland and Britain.

After the Department of Agriculture became aware that burgers from two Irish processors were found to contain horse meat and traces of pig meat, vets were sent in to establish how it happened.

They took samples and carried out tests at the two plants involved; Silvercrest Foods in Ballybay and Liffey Meats in Ballyjamesduff.

Elsewhere, Tesco has taken out prominent adverts in most newspapers stating: "We and our supplier have let you down and we apologise."

Britain's food watchdog, the Food Standards Agency, is considering whether legal action should be taken against companies at the centre of the scandal.

Minister of State for Agriculture and Food in Britain David Heath has said there may be criminal proceedings following the discovery of horsemeat in beef burgers there.

He was answering an urgent question in the House of Commons on the British government's response to the finding of horse meat in supermarket meat products.

The British Labour Party wanted to know why the discovery was not made by food standard authorties in Britain.