Dissident republicans in Northern Ireland tried to use a truck bomb to blow up a ferry sailing to Scotland on Brexit day, police said.

Officers linked a ferry crossing of the Irish Sea on 31 January with a bomb found on a heavy goods vehicle in county Armagh earlier this week.

The Police Service of Norther Ireland (PSNI) believes the Continuity IRA (CIRA), a splinter group that rejects the peace process, was responsible for the device.

George Clarke, assistant chief constable, told reporters that a phone call was made to a media outlet on 31 January warning that there was a bomb on the trailer of a lorry at Belfast port that was due to sail to Britain.

It was a “viable device”, he said. “It could have caused death and very serious injury and harm to members of the public. Those who planted this device were reckless or intended to cause that level of harm.”

Clarke said those responsible planned for the device to explode at around the time the UK left the EU – a claim rejected by sources close to dissidents.

After the phone warning, police searched truck trailers but found nothing and the ferry sailed as planned without incident, he said.

On Monday there was a second phone call to the media outlet, which prompted police to mount a two-day operation involving the search of 400 vehicles, leading to the discovery of a bomb attached to a truck in the Silverwood Industrial Estate in Lurgan. Army bomb disposal officers made it safe.

Det Supt Sean Wright, from the PSNI’s terrorism investigation unit, told a press conference that dissident republicans had shown reckless disregard for life.

“Had this vehicle travelled and the device had exploded at any point along the M1 [in Northern Ireland], across the Westlink or into the harbour estate, the risks posed do not bear thinking about. The only conclusion that we can draw is that once again dissident republicans have shown a total disregard for the community, for businesses and for wider society.”

Sinn Féin’s policing spokesman Gerry Kelly told PA there could have been “catastrophic loss of life” if the device had detonated on board a ferry.

Alan Chambers, an Ulster Unionist party’s policing board representative, said the bomb showed the dissidents did not care whom they put at risk. “The consequences could have been horrendous.”

However sources close to republican dissidents in Belfast challenged the police version that the bomb was meant to explode during a ferry crossing.

They said the Continuity IRA instead was following standard armed republican tactics of transporting bombs over to England to 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.

“The idea that anti-Good Friday Agreement republicans were going to blow up a ship to mark Brexit day is nonsense and propaganda,” the republican sources told the Guardian.

Dissidents opposed to the peace process have staged attacks since well before Brexit. However dissident republicans linked with another splinter group, the Real IRA, have previously called the UK’s departure from the EU a “huge help” to Irish republicanism, saying it would fuel violent resistance to British rule in Northern Ireland.

There were at least five attacks on security forces last year, which prompted Simon Byrne, the chief constable of the PSNI, to express concern at the “tempo and pace” of attacks and to warn that a hard border imposed by a no-deal Brexit could “trigger” other people to join dissident ranks.

In a separate development, Conor Murphy, Sinn Féin’s minister for finance in the Stormont government, faced calls to resign over comments he made in 2007 about Paul Quinn, a 21-year-old man beaten to death by a gang that allegedly included IRA members.

Murphy this week apologised for having accused Quinn of being a criminal, a claim that recently resurfaced and tripped up Sinn Féin’s leader, Mary Lou McDonald, on the eve of Saturday’s general election in the Irish republic. McDonald was due to speak with Quinn’s parents on Thursday night.