The Continuity IRA was responsible for planting a ‘Brexit day’ bomb on a lorry trailer in Co Armagh last week.
In a statement to the Irish News the republican group said the device was timed to coincide with Britain’s exit from the EU.
It was discovered after searchest the Silverwood Industrial Estate in Lurgan on Tuesday and later made safe by the British army bomb squad.
Temporary assistant chief constable George Clarke last night said the device was “viable”.
The bomb was attached to a refrigerated trailer belonging to a haulage firm based at the industrial estate.
It is believed the republican group expected the trailer carrying the bomb to be transported to Belfast docks where it would then be loaded onto a passenger Ferry destined for Scotland.
The group said the device was timed to detonate at the docks around the same time the UK formally left the EU last week.
In a coded bomb warning received by the Irish News last Friday night, the Continuity IRA said that a “live device” was in a lorry at Belfast docks and that it was due to travel on a passenger ferry at midnight.
Police said yesterday that after receiving the warning they carried out checks at the docks “and worked with the ferry company, Belfast Harbour authorities and Police Scotland to try to locate that device” but nothing was found.
The ferry later sailed to Scotland arriving safely, police say.
In a second statement to the Irish News on Monday, again using a recognised codeword, the group provided more detail about the bomb.
It claimed that a live device had been attached “with magnets underneath a refrigerated trailer belonging to” a named transport firm.
It said that the trailer had been loaded in north Armagh.
It has since emerged that firm is based at the Silverwood Industrial Estate.
The group claims the device was on a timer and was similar to others used by the Continuity IRA in recent months.
The CIRA warned that the chance of the device “dropping off” the trailer were slim.
“It was timed for Britain’s exit from the EU and to bring attention to the sea border,” the statement added.
Police say that the fresh information “enabled police to conduct focused investigations with the haulage company”.
They say that throughout the evening of Monday and Tuesday “police and the haulage company eliminated in the region of 400 vehicles in order to locate the explosive device”.
They say it was “subsequently found attached to a heavy goods vehicle” at the industrial estate.
Mr Clarke said the device “could have caused death and very serious injury and harm to members of the public”.
"If the device was planted on a Friday, it was between Friday and Monday before they gave us the information that enables us to locate this (device),” he said.
"During that period of time, a viable bomb is in a commercial yard posing a significant risk to anyone who comes within range of it."
SDLP Policing Board member Dolores Kelly condemned the attempted attack.
“We cannot become complacent about the threat that dissident republicans pose and their desire to kill people in our communities in the pursuit of an outdated ideology that has been rejected by the people of Ireland.”
First Minister Arlene Foster said: “The potential damage which could have been caused and loss of life either here in Northern Ireland, on board a ferry or in Great Britain do not bear thinking about.
UUP assembly member Doug Beattie described the attack as a “national security threat”.
“Without a doubt it was an attempt to isolate Northern Ireland from the rest of Great Britain by creating a threat to on-board ferry traffic,” he said.
Local Sinn Féin councillor Catherine Nelson described the attack as “reckless”.
Policing Board chair Anne Connolly also condemned the attack.
