A mortar device pointing skywards was found near the south Armagh village of Cullyhanna.
Police believe the device may have been set up by dissidents opposed to the peace process in an attempt to down a helicopter.
The discovery prompted a large security operation, with an army bomb disposal team carrying out a controlled explosion. Two dark-coloured tubes around 10ft long and resembling drain pipes were observed at the scene.
In March, a mortar attack on a police station in Londonderry was foiled after police stopped a van with four viable devices primed and ready to launch. Mortars have also been found in Belfast.