A security operation is under way in Ballycastle, County Antrim and part of the town has been cordoned off.
The RUC blocked off Castle Street after receiving a telephoned warning that a device had been left in the area.
An army technical officer has been called to the scene.
Thousands of people are expected to travel to the town today for the Old Lammas fair.
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The RUC has advised visitors to avoid the Coleraine road and use either the Whitepark road or the Straid road instead.