The device was primed and “ready to be used”, according to gardaí. They said it was the first discovery of a mortar in such a state of readiness in some time.
Gardaí believe the interception of the car, a Northern Ireland-registered Peugeot 306, prevented a possible dissident republican attack.
A Garda source said the mortar could have caused destruction similar to that done in an 1985 IRA mortar attack on Newry police station that killed nine RUC officers.
It took over four hours in freezing temperatures to make the device safe, and gardaí were forced to close off the M1 in both directions as the mortar could have posed a significant threat to the public.
