Weapons and explosive devices have been uncovered as part of an investigation into dissident republican activity in the border region.
Searches were carried out in the Scotstown area of Co Monaghan last Wednesday.
A number of firearms, including AK-47 assault rifles, mortars, detonators, detonating cord and other component parts of Improvised Explosive Devices (IEDs).
Gardaí believe some of the weapons may have originally belonged to the provisional IRA but were moved before they could be decommissioned.
A 43-year-old man was arrested in the Scotstown area on 25 November and appeared before a special sitting of the Special Criminal Court on Saturday.
Jim Smyth, with an address at Aghalissabeagh, Scotstown, Co Monaghan, was charged with membership of an unlawful organisation, styling itself the Irish Republican Army, otherwise Oglaigh na hÉireann, otherwise the IRA.
He was remanded custody until tomorrow morning, when a bail application is expected to be heard.
GardaÍ say the search operation as part of the investigation is ongoing.