GARDAI have been called in to investigate as the horse meat scandal spread to both sides of the border – with up to 75pc equine DNA found in imported beef product.
An Irish meat trader is now at the centre of the probe, which will deal another hammer-blow to Ireland's increasingly fragile reputation.
Supermac's beef burger supplier Rangeland Foods in Castleblayney, Co Monaghan, became the latest plant to suspend production after 75pc horse meat was found in product there.
And the crisis deepened when separate tests done by UK authorities at Freeza Meats in Newry found two samples of frozen product contained as much as 80pc horse meat.
Agriculture Minister Simon Coveney, who has been under massive pressure on the horse meat issue, was hoping the damaging revelations were over.
But the controversy reached new heights as the levels of equine DNA are far higher than recorded in previous tests – and the gardai and fraud squad were called in.
Previous results had peaked at 29pc horse meat found in a Tesco burger during the first batch of tests by the Food Safety Authority, made public in January.
However, all of the suspect meat is understood to be linked, with Mr Coveney stressing he believes the "same product" is involved.
The family-run Rangeland Foods plant is 6km away from Larry Goodman-owned Silvercrest Foods in Ballybay, which had been at the centre of the fallout so far.
And the UK Food Standards Agency said that the horse meat found at Freeza Meats is potentially linked to the Silvercrest factory in the Republic of Ireland.
The cross-border probe is now focusing on what connects the various meat plants involved, with special attention given to Polish imports.
Mr Coveney announced a major ramping up of the investigation and has called in the gardai and his department's own Special Investigation Unit to help with inquiries.
Production at the Rangeland processing plant in Castleblayney, which employs almost 100 workers, has now been suspended.
Rangeland promises "full product traceability from farm to plate" and says 90pc of its beef is of Irish origin.
It is understood that the affected batch of meat was not intended for use in burgers for Supermac's, which has launched a high-profile advertising campaign championing its 100pc Irish beef burgers, but now finds itself embroiled in the controversy.
Instead, the rogue consignment of meat was going to be used in products intended for the catering market abroad.
Last night, Supermac's insisted it remained confident that its burgers had not been affected by the new horse meat discovery.
But the entire beef industry in Ireland has been looking closely at its own supplies since the Department of Agriculture first blamed Polish product for previous horse DNA finds.
This is why Rangeland carried out its own tests, which detected equine DNA, and alerted the Department of Agriculture last Thursday evening.
It said the tainted consignment was received in early January, and stressed that it did not go into production of food.
Last Friday, inspectors moved into the plant to carry out their own tests, which confirmed horse DNA was present at a level of 75pc.
Mr Coveney, who has been fighting fires on the scandal for the past three weeks, published the new test results last night.
"The investigation is focusing on the full supply chain including the meat trader concerned and others who facilitated the purchase of the product and its transfer to users in Ireland," he said.
Despite tests in Poland so far coming back negative, Mr Coveney said he was confident of the source of the meat – and now it was a question of identifying how it came to contain horse.
The horse burger investigation has now widened to two separate Polish suppliers and an Irish-based meat trader, the Irish Independent has learned.
The department says the decision to send in the gardai and its Special Investigation Unit shows how seriously it is taking the investigation.
The gardai are expected to begin looking through documentation attached to the sales of the product. The British food safety agency is also looking at the role of the meat dealer.
A spokesman for Rangeland said, as of yesterday evening, it had temporarily suspended the production of beef at its Castleblayney plant.
Farmers reacted furiously to the latest finding of horse DNA.
Gabriel Gilmartin, president of the Irish Cattle and Sheep Farmers' Association, described the findings at Rangeland Foods as "a deeply worrying development".
"It suggests that the minister will now have to move quickly to investigate all meat processing plants," he added.