Restrictions were imposed yesterday on a farm on the north Antrim coast after a new foot-and-mouth alert in Northern Ireland.
Sheep in Co Derry were also slaughtered after some of them showed signs of the disease.
There have been no new cases in the North since the fourth was confirmed at Ardboe, Co Tyrone, three weeks ago.
Blood tests carried out on sheep at a farm at Murlough Bay, near Ballycastle, found symptoms similar to the virus.
Eighteen of the 325 sheep on the farm are showing lesions consistent with foot-and-mouth and samples have been sent to laboratories in Surrey for testing. A 3 km precautionary control zone has been set up around the farm.
The Stormont Agriculture Minister, Ms Brid Rodgers, said: "These symptoms are giving some cause for concern and samples have been sent to Pirbright for analysis. Results on these tests are not expected for another few days."
Tests on a flock of 64 sheep on a farm near Magherafelt, Co Derry, have also shown positive initial screenings.
Ms Rodgers said this didn't mean the flock had foot-and-mouth, but that it may have been exposed to the virus at some stage in the past.
"Therefore, and on veterinary advice, I have decided to cull that flock as a precautionary measure. The flock owner has been informed and the animals will be slaughtered and rendered."
In Dublin yesterday, the Minister for the Marine and Natural Resources, Mr Fahey, said that the requested suspension of all field-based exploration activities for minerals by prospecting licence-holders would be lifted from tomorrow.
A new case of foot-and-mouth was confirmed yesterday in Powys, mid-Wales, a Welsh Assembly spokeswoman said. It brings the total number of cases in Wales to 87.