The Continuity IRA has admitted it tried to smuggle a bomb onto a lorry destined for an Irish Sea ferry.

In a statement issued to the Irish News in Belfast the republican terror group said it had planned for the bomb to go off on the day the UK left the EU.

The explosive device was discovered after police searches on the Silverwood industrial estate in Lurgan, County Armagh on Tuesday. The bomb, which a senior police officer described as “viable”, was made safe by the army bomb disposal squad.

The bomb had been attached to a refrigerated trailer belonging to a haulage firm based at the site.

It is understood the Continuity IRA (CIRA) planned to smuggle the bomb across the Irish Sea on a ship destined for Scotland. It would then be transported to an unknown location in England on the day the UK left the EU.

CIRA said the bomb had been attached to the lorry “with magnets underneath a refrigerated trailer”.

The dissident group said the bomb was on a timer and was similar to others used by its operatives in recent months.

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 CIRA statement added.

The PSNI later released images of a device, comprising of a number of parts including wires, which police recovered from a lorry.

The bomb that police believe was intended to explode on Brexit night. Photograph: PSNI/PA

Det Supt Sean Wright said the images “demonstrate the sheer recklessness” of those behind the plot.

“Today I am releasing two photographs of the device found attached to a heavy goods vehicle in the Silverwood Industrial Estate,” he said. “These images clearly show the explosive device attached to the lorry. They also demonstrate the sheer recklessness of those who knowingly put the driver, road users and the wider public at risk of death or serious injury.”

On Wednesday sources close to republican dissidents in Belfast challenged suggestions by police that the bomb was meant to explode during the ferry crossing.

They said CIRA was following standard armed republican tactics of transporting bombs over to England to attack commercial or strategic targets.

“The plan was no different, although far smaller in scale, than the way the Provisional IRA smuggled the huge bomb that devastated Canary Wharf in 1996. There is no way republicans were planning to explode a bomb on a ferry.”

The Canary Wharf bomb, which signalled the end of the Provisional IRA’s 1994 ceasefire, was built by operatives from its East Tyrone Brigade and then transported in a lorry by activists from PIRA’s South Armagh Brigade.

Dolores Kelly, the SDLP Northern Ireland Policing Board member and representative in the Stormont assembly for the area where the bomb was found, condemned the attempted attack.

She said: “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.”

Arlene Foster, the Northern Ireland first minister, 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.

The Ulster Unionist assembly member Doug Beattie described the bomb plot 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.

Catherine Nelson, a Sinn Féin councillor in north Armagh, also described the attack as “reckless”.