Northern Ireland's chief vet has said authorities there and in the State were concerned that responsibility for the State's first outbreak of foot-and-mouth disease lay with an unidentified flock of sheep infected with the virus.
Mr Bob McCracken said he did not believe the sheep which was confirmed to have had the disease in South Armagh at the end of last month was directly responsible for the outbreak a few miles across the border in Co Louth.
He said the situation was being monitored on both sides of the border.
"We certainly don't believe this virus came direct from the Meigh farm to this farm. It far too long of an interval, 21 days," he said.
"So the concern on both sides of the border is that there is a third flock somewhere that is infected, probably from the Meigh farm, which has in turn infected the farm in Co Louth.
"That is our supposition at the moment and that is what we are, on both sides of the border, pursuing with considerable urgency."
The sheep which was confirmed positive in South Armagh was from a consignment of sheep taken illegally into Northern Ireland from Britain before the foot-and-mouth outbreak was known about anywhere in the UK.
There has been considerable confusion about just how many sheep were brought in and the Department of Agriculture in Belfast has said there could be between 30 and 60 sheep unidentified.
There was concern tonight that that some of those sheep might have been hidden in the border region and could be responsible for the latest outbreak.
PA