An Irish food factory's production has been suspended after new tests revealed horse DNA in its frozen burgers.
The ABP Food Group said it had halted work at its Silvercrest Foods plant, in Co Monaghan, until further notice.
The firm said it believed the contamination had come from one supplier - after further results from the Irish Department of Agriculture.
On Tuesday, Irish food inspectors said they had found horse DNA in burgers sold across UK and Irish supermarkets.
Officials from the Republic of Ireland's food safety authority (FSAI) confirmed the meat had come from Liffey Meats and Silvercrest Foods, in Ireland, and the Dalepak Hambleton processing plant in Yorkshire.
The contaminated food - some of which was also found to contain pig DNA - was on sale in Tesco, Iceland, Lidl, Aldi and Dunnes stores.
The ABP Food Group - one of Europe's largest processors and suppliers - said that, as a result of new tests two days ago, "the responsible course of action is to suspend all production at the Silvercrest plant in County Monaghan with immediate effect".
The firm had already recalled from supermarkets some 10 million burgers thought to contain horsemeat, which are due to be destroyed.
Commenting on the latest results, Ireland's Agriculture Minister Simon Coveney said seven samples of raw ingredients had been tested, including one sourced from another European country that had tested positive.
But all ingredients in burgers sourced from Irish suppliers had tested negative for horse DNA, he said.
A statement released from his department added: "Thirteen samples of finished burgers were tested for the presence of equine DNA.
"Nine have tested positive for traces of equine DNA and another four have tested negative.
"The minister and the FSAI have repeated their clear statement that there is no concern from a food safety perspective."
'Matter of criminality'
Positive samples are set to be analysed further, in order to quantify the percentage of horsemeat present.
Meanwhile, the Food Minister in Westminster, David Heath, said on Thursday that the contamination of meat sold in the UK and Ireland was "almost certainly a matter of criminality" and it was possible prosecutions could take place.
The supermarkets involved in selling contaminated products have said they are looking into the matter and have withdrawn affected items.
On Thursday, Tesco took out adverts in British newspapers apologising and promising to investigate.