Gardaí have uncovered ammunition in a series of ongoing searches on premises and houses in Sligo.
The army explosives unit has been brought in to assist Gardaí, who also discovered a quantity of materials which they believe to be explosives.
One person has been arrested under section 30 of the Offences Against the State Act.
They are being questioned at Sligo Garda station.
Gardaí say the searches are ongoing in the area.