Detectives from the PSNI's serious crime branch have carried out a search in the Crossmaglen area.
The search was part on an ongoing operation with An Garda Siochana in relation to terrorist activity.
A number of items have been recovered for examination including a rifle and ammunition.
Irish police investigating dissident republicans arrested five men 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 are still being questioned.
Gardai stopped a car on Ecco Road in Dundalk at about 1125 BST on Sunday 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.