A van bomb packed with 600lbs of homemade explosives and abandoned near the Irish border could have caused substantial damage and major loss of life, police have said.
A senior officer said the bomb was primed and "ready to go" and could have had a devastating impact if it had detonated.
The white Citroen Berlingo van was spotted by a member of the public on Thursday evening after it was abandoned on a border road outside Newry in Northern Ireland.
The security operation on the vehicle only ended late on Friday night and District Commander Chief Superintendent Alasdair Robinson said it could have easily claimed lives.
"The device contained two blue barrels with 125kg of homemade explosives in each one, and a detonator - all the equipment which meant this device was ready to go," he said. "To explain it, there was 600lbs of explosives. This was a very significant device. If this had exploded it would have caused devastation."
Dissident republicans opposed to the peace process are being blamed for the failed attack and there is speculation the device could have been destined for a town centre or a security target. The same groups have been linked to the discovery of a smaller explosive device, plus a weapons cache, in north Belfast on Friday night.
The incident was widely condemned, with unionists expressing concern over dissident activity and Sinn Fein calling for the groups to end their campaign which the party said had no support.
Newry's courthouse was damaged by a major car bomb in 2010, but Mr Robinson said the latest find was twice as big as the bomb used in that attack. He said of the van bomb: "To put it in perspective - anyone within 50 metres of this device would have been killed and anyone within 100 metres seriously injured."
The alert was raised when the vehicle was spotted abandoned, with its engine running, on the Fathom Line road outside Newry on Thursday. Mr Robinson said the likely target and the reason for the device being abandoned were unclear. But the senior officer said the presence of regular police patrols had forced bombers to abandon devices in the past.
Asked about the scale of the threat posed by dissident republican groups, the chief superintendent said: "This is the third attack in the Newry area over the last few weeks, however we have dealt with all three of these attacks. Officers are out in the community day and night, doing their utmost to ensure that the community is safe and we will continue to do this."