An army bomb disposal team carried out a controlled explosion today on a mortar found among a haul of dissident republican weaponry.
The continuing security operation in Co Louth came as, in a separate development, police in the North arrested four men after recovering a gun and ammunition in Co Tyrone.
The arrests were made after police stopped a car in the Cookstown area late last night.
The weapon and ammunition were found when the police searched the vehicle. The four men were taken to Antrim police station for questioning.
The security operation continued south of the border, where a major dissident republican explosives dump and arms cache was uncovered.
An improvised mortar, three kilos of TNT, bomb-making equipment and a pipe bomb were found hidden in Barmeath woods near Dunleer in Co Louth.
The weapons haul included a general-purpose machine gun, a shotgun and assorted ammunition.
The arms were packed into barrels and buried.
The Louth finds were the second blow to suspected factions of the Real IRA in recent days and followed 10 arrests and separate searches over the weekend.