A rifle and ammunition have been found during a police search in Crossmaglen, south Armagh.
PSNI detectives carried out the search as part of an ongoing operation with police in the Irish Republic in relation to terrorist activity.
Five dissident republican suspects were arrested in County Louth on Sunday.
A handgun, a shotgun, components of an explosive device and ammunition were seized in follow-up searches in County Louth and County Monaghan.
Six vehicles were also seized.
The five men arrested on Sunday are still being questioned.
Police stopped a car on Ecco Road in Dundalk at about 1125 BST and a gun and a balaclava found. Two men, aged in their mid-20s and mid-30s, were arrested.
Ten minutes later, a car was stopped about 12 miles away in Ardee. Ammunition and a balaclava were found.
Three men, whose ages range between their early-30s and mid-50s, were arrested.