Police and politicians blamed Irish Republican Army dissidents for the device in the city of Armagh. Police thanked members of the public for tipping them off to the location of the concealed device.

IRA-engineered "horizontal" mortars are designed to fire a mortar shell at close range into the side of a passing police or army vehicle.

Police said the suspect was arrested Friday and is being questioned at their interrogation center west of Belfast.

Two breakaway IRA factions are defying the outlawed group's 2005 decisions to renounce violence and disarm.