Lambs processed at a Co Roscommon factory last Tuesday are from the same load identified by the Northern Ireland Agriculture Minister yesterday as likely to test positive for foot-and-mouth disease.
The 248 lambs processed at the plant are believed to have passed through the farm at Meigh, Co Armagh, which the Northern authorities believe contain a positive case of the disease.
Meanwhile, a further nine cases of the disease were confirmed in the UK yesterday, bringing the total to 27. Four of the new cases are in Wales.
The EU Commissioner for Food Safety, Mr David Byrne, said yesterday there was no basis as yet for extending the ban on meat and dairy exports to the Republic. But, he said, the situation was changing "hour by hour" and he would not shy away from imposing a ban on the Republic if it was needed.
"It would obviously cause me pain if it did arise. There is no evidence that such a ban is required. But I have to be absolutely even-handed in my duties as a commissioner," he said.
Last night, Ms Brid Rodgers, the Northern Minister for Agriculture confirmed, following preliminary tests at Meigh, she believed the suspect sheep had suffered from the disease.
A Department of Agriculture spokesman in Dublin said last night their investigators believe the sheep came into the Republic from the Co Armagh farm which was supplied from Britain.
The statement came following an admission from Kepak, Athleague, that 248 lambs delivered to it on February 20th were not the property of the farmer in whose name they were supplied.
It said it had been told by Department of Agriculture investigators on Monday the lambs may have originated in Northern Ireland or the UK. "It has come to light following investigations by the Department of Agriculture into the transport of animals across the Border that the lambs in question were not the property of the farmer in whose name they were supplied," said the statement.
As a result the Department of Agriculture placed 12 farms belonging to farm operatives and holding pens belonging to the factory, under surveillance.
The Department of Agriculture spokesman said he was still confident that despite the link to the Armagh farm, the disease could be kept out of the Republic because the lambs had only been on the premises for a few hours before being slaughtered.
He said the Department wanted to interview the man who had delivered the sheep to Athleague. However, he is understood to be outside the jurisdiction.
The Northern authorities said a consignment of 200 sheep was bought at a market in Carlisle, England, over a week ago - before the disease was confirmed in Britain - and transferred to Northern Ireland for slaughter.
Instead of being slaughtered, however, Department of Agriculture officials yesterday traced a number of them to a farm in Meigh, near Newry.
Ms Rodgers ordered the farm, which straddles the Border, to be placed under restriction and have an eight-kilometre surveillance zone established around it as a precautionary measure.
It is believed most of the sheep from the suspect consignment may have ended up in the Republic.