Two former Northern Ireland police chiefs have warned that dissident republicans are ready to exploit the chaos around Brexit to launch a new wave of terror.
It comes amid growing fears of violence linked to the UK's impending departure from the European Union on March 29.
Former Assistant Chief Constable Alan McQuillan told this newspaper that some are "hitching themselves to the Brexit bandwagon" to stoke trouble.
His warning came as former PSNI boss Hugh Orde said dissident republicans would view a hard border as an opportunity to mount further attacks.
It also follows reports that MI5 has stationed more than 700 officers in Belfast as part of an intelligence operation to combat the growing threat.
The spy agency's main target is the so-called New IRA, a group of some 40 hardliners responsible for the Londonderry courthouse car bombing last weekend.
That explosion occurred only 30 minutes after a telephone warning to the Samaritans in the West Midlands while police were still clearing the area.
Mr McQuillan said the hardliners remain a threat and are intent on further attacks despite the sustained security push by police and intelligence services.
"The reality is they are always dangerous and they will use fears over a hard border to try and ramp up their activities," he said.
"The dissidents are hitching themselves to the Brexit bandwagon. I think there will be further attacks, I think they remain dangerous. But I don't think they'll succeed."
He added: "They're destroying the lives of Derry people. Let's be honest, it's not damaging people in Dublin or London. Derry last week damaged people in Derry."
He described the New IRA, formed in 2012 by a merger of the Real IRA which carried out the 1998 Omagh bombing, splinter groups and individuals, as "utterly, utterly reckless".
He added: "Phoning England with a bomb warning introduced a huge delay and it ran the risk of police not having time to evacuate and the bomb going off and killing people. It was a recipe to create another Omagh."
Mr McQuillan said the New IRA's ability to launch last Saturday's attack was "down to police resources" and he said the current number of officers - around 6,500 - falls well below the 7,500 recommended in the Patten Report.
"Police can't be everywhere all the time," he said.
"Thinking back to my service, there were times when you knew there was a general intention to mount an attack in a particular area and you did everything you could to prevent that.
"Sometimes it worked and sometimes it didn't. You couldn't stop every single thing getting through. Alternatively, if you're directing your resources towards one thing, the terrorists will often have a secondary target and they'll go for that instead.
"PSNI has been run down in staffing levels and budget over a number of years by successive governments, but we're entering a dangerous phase now and they need to make sure that PSNI has all the resources it needs to deal with this."
It came as former Chief Constable Sir Hugh also warned that a hard border would be exploited by dissident republicans. He accused politicians of not paying enough attention to the potential for a return to violence in the even of a hard border and he said there is no way to avoid the return of security patrols in the event of a no-deal Brexit.
"At the moment you see anything that starts to create the perception of a hard distinction between North and South, it creates a catalyst that allows people to exploit that position and dissident republicans would be in that category," he told RTE's This Week programme.
He described last weekend's New IRA car bombing as a "significant move".
He added: "It's a statement that things are going to get more difficult, not less."
Sir Hugh said that, if he was still leading the PSNI, a hard border would "worry me greatly".
Asked whether politicians had paid enough attention to the security threat that looms over a hard border, he replied: "People seem to have their head stuck in the mud and hoping it will all go away, and certainly it won't and it hasn't."
PSNI Chief Constable George Hamilton warned last year that if border posts and security installations were created as a result of a hard Brexit they would be seen as targets for attack by dissident republicans.
"The last thing we would want is any infrastructure around the border because there is something symbolic about it and it becomes a target for violent dissident republicans," he said.
"Our assessment is that they would be a target because it would be representative of the state and in their minds fair game for attack. I would assume that that assessment is shared by senior politicians and officials who are negotiating Brexit."
Garda Commissioner Drew Harris, a former high-ranking PSNI officer, also warned in November that dissident republicans will attempt to exploit any form of a hard border post-Brexit as "an emotional rally call around their outlook and terrorist aspirations".