Fourth arrest over Dundalk mortar
Four men have been arrested after an explosive device was found in a car near Dundalk, County Louth.
The device, described by police as a viable mortar, was made safe by bomb disposal experts at around 2130 GMT on Tuesday.
The discovery was part of an operation by police investigating the activities of dissident republicans.
Two men were arrested at the scene, both in their 20s, and two in their 30s were arrested nearby.
Two of those arrested are said to be from Northern Ireland, and another is from Dundalk.
The M1 motorway was closed in both directions while an Army team carried out what was described as " a technically difficult task that took over four hours".
Irish police said the mortar "posed a significant threat to the public".
In a follow up search a property was searched in Drumiskin, near Dundalk.
A number of items were seized and are being examined.