A major food factory has suspended all production after horse DNA was found in frozen burgers in new tests just two days ago.
The ABP Food Group, one of Europe's biggest suppliers and processors, revealed it has stopped work at its Silvercrest Foods plant in Co Monaghan, until further notice.
The firm said that, following new results from the Department of Agriculture, it believes the source of the contaminated material is one supplier.
It said: "However, because equine DNA has been found in finished products tested this week, we have decided that the responsible course of action is to suspend all production at the Silvercrest plant in County Monaghan with immediate effect."
Ten million burgers suspected of containing some levels of horse meat were cleared from several supermarkets freezers across Ireland and the UK this week and are expected to be destroyed.
Agriculture Minister Simon Coveney revealed that seven samples of raw ingredients were tested, including one sourced from another European country which tested positive.
All ingredients in the production of burgers sourced from Irish suppliers tested negative for equine DNA.
"Thirteen samples of finished burgers were tested for the presence of equine DNA," said a statement. "Nine have tested positive for traces of equine DNA and another four have tested negative."
The minister and Food Safety Authority of Ireland (FSAI) have arranged to have the positive samples analysed further in Germany with a view to quantifying the percentage of equine DNA present.
"The minister and the FSAI have repeated their clear statement that there is no concern from a food safety perspective," the statement added.