Northern Ireland police say a "significant" bomb was found near the main Dublin-to-Belfast motorway on Friday, the anniversary of a peace deal that largely ended three decades of sectarian violence.
The A1 between Newry and Dublin was closed briefly to allow a bomb disposal team to clear the device which police said had the potential to cause fatalities.
A police source told Reuters that investigators believed the attack may have been carried out by dissident Irish nationalists opposed to the Good Friday Peace Agreement of 1998 and may have been intended to hit a passing police patrol.
The agreement largely ended more than three decades of violence between mainly Catholic Irish nationalists opposed to British rule of Northern Ireland and predominantly Protestant unionists who wanted it to continue.
However, dissident nationalists opposed to the deal still mount sporadic gun and bomb attacks.