Christmas shoppers have been warned that rival dissident republican terror groups are competing to pull off attacks in towns and cities across Northern Ireland.
Police revealed there has been a surge of dissident activity in recent months, with the rogue terror groups "intent on causing death and disruption".
Security checkpoints have already been put in place throughout Belfast, described as a "premium target", and the PSNI is set to ramp up its presence in towns across the region.
Assistant Chief Constable Will Kerr said there had been an uplift in the lethal capability of various dissident groupings.
"I think the fact we are putting out a statement that we assess there is a strong possibility that violent dissident republican groupings will attempt to carry out attacks in towns and cities throughout Northern Ireland will give you a strong sense of how concerned we are about this issue," Mr Kerr said.
"At this stage we know - we believe it is a strong possibility - that a number of those groups are intent on carrying out attacks across Northern Ireland. That is why we are putting out this public appeal for patience, for vigilance, for information and support over the Christmas period."
Police would not outline any intelligence they may have of specific threats in the run-up to Christmas. They said information from the public was crucial to fight the threat.
"There will be significant numbers of police officers deployed across Northern Ireland," Mr Kerr said.
"We want to provide that visible reassurance if you are out socialising, Christmas shopping or spending time with family. We don't want to cause disruption and do the job of these people for them."
Mr Kerr said the dissident factions remained "unwanted remnants of the past" with the intent and capability to do serious harm.
He said police had recorded a number of recent successes in operations against dissident groups.
He added: "In some areas there is a better degree of co-operation between them.
"In some areas there is also a degree of competition between them, and certainly we'll see that in the run-up to Christmas."
Attacks last Christmas included a car bomb at Victoria Square, an incendiary device in a golf outlet and an explosion in the Cathedral Quarter area on a Friday night when it was thronged with revellers.
Police checkpoints were set up throughout Belfast a fortnight ago, with thousands of vehicles stopped so far.
"There is no such thing, of course, as a perfect security solution to these threats. We're always trying to get the balance right between managing the threat, keeping people safe and not causing them disruption," Mr Kerr said.
"The vast majority of people are just trying to enjoy the Christmas period."
Mr Kerr said police were urging the public to be vigilant in the coming weeks and to be patient.
Meanwhile, detectives from Serious Crime Branch investigating dissident terrorist activity have arrested a 55-year-old man in Londonderry.
Detective Superintendent Kevin Geddes said: "The suspect was arrested in the Creggan area of the city this morning and has been taken to the Serious Crime Suite at Antrim police station for questioning.
"In addition, two properties were searched during this morning's operation."
Police will mount more vehicle checkpoints across Northern Ireland during the festive season while uniformed and plain-clothed patrols will also be stepped up.
Assistant Chief Constable Will Kerr stressed the need for public co-operation to thwart the dissidents.
He described the extremists as an "unrepresentative remnant of a past that no one wants to return to". "But they remain a dangerous remnant," he said.
He warned that police had witnessed an upsurge in the level and intensity of dissident attacks in recent months.