Police in Northern Ireland say they are investigating a potential plot by Irish Republican Army dissidents to blow up a truck crossing the Irish Sea on the day Britain left the European Union last week.

The Police Service of Northern Ireland said it had received a report that there was a bomb on a truck at Belfast docks that was due to board a ferry to Scotland on Jan. 31, which was Brexit day.

Despite a search, nothing was found. But on Tuesday, after another tip, police found a bomb aboard a truck at an industrial park in the Northern Ireland town of Lurgan. Police said on Feb. 6 that they want to speak to anyone who noticed suspicious activity in the area on Jan. 31.

“It is clear from the information available to police that dissident republicans deliberately and recklessly attached an explosive device to a heavy goods vehicle in the full knowledge and expectation that it would put the driver of that vehicle, road users and the wider public at serious risk of injury and possible death,” said Detective Superintendent Sean Wright of the Terrorism Investigation Unit.

More than 3,700 people died during decades of violence before Northern Ireland's 1998 peace accord. Most militants have renounced violence, but small groups of dissidents continue to carry out occasional bombings and shootings.

The violent dissidents were emboldened by several years of political drift in Northern Ireland, whose power-sharing government was suspended between January 2017 and last month —  and by uncertainty about the future of the currently invisible border between the U.K.'s Northern Ireland and EU member Ireland after Brexit.