Gardaí have launched a large-scale search on lands in the Burt area of Co Donegal.
Both detectives and uniformed officers are taking part in the search which is based around a rural farm on the Inishowen Peninsula.
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The army has also been drafted to take part in the operation.
Garda vans arrived at the location earlier on Thursday and commenced search of a number of out buildings and sheds.
Local gardaí and officers from outside the local jurisdiction are at the scene.
The main road into the farm has now been blocked as the unidentified operation continues.
Gardaí are remaining tight-lipped about the nature of the searches.
A spokesperson said "An Garda Síochána does not comment on ongoing operational activity."