The growing range of bomb-making techniques employed by dissident republicans is of great concern, police chiefs warned today.
Increasing co-operation among the renegade groups opposed to the Northern Ireland peace process is also a serious worry, officers from both sides of the border said.
Police Service of Northern Ireland Assistant Chief Constable Judith Gillespie and Garda Commissioner Fachtna Murphy provided the update on the dissident threat at a cross-border conference in Belfast where they were joined by Stormont justice minister David Ford and his counterpart in the Republic Dermot Ahern.
Mrs Gillespie said the size of the groups is not the most significant element.
"It's probably more appropriate to talk about their capability and we certainly are concerned at a growing capability," she said.
"We have seen an increase in technical expertise and the successful detonation of improvised explosive devices, the range of techniques they are now using - and that is of great concern.
"And we have also seen groups working more closely together than we have seen in the past and that's also of serious concern."
Dissidents have been responsible for a number of car bomb attacks against security force targets in Northern Ireland this year.
Mrs Gillespie's warning comes weeks after the security services raised the threat level of a dissident attack in mainland UK from moderate to substantial.
Mr Murphy said garda intelligence corroborated the decision to upgrade the warning level.
"I have no reason to say that the threat assessment as categorised in the UK is anything but correct," he said.
He added that the dissidents in the Republic are a "small group of focused people".
"We are actively targeting them and we are actively engaged in sharing information, sharing intelligence and working closely with our colleagues in Northern Ireland to prevent and stop a small group of people."
The seminar at the La Mon hotel in the east of the city focused on cross-border efforts to tackle organised crime.
Mr Ford hailed the co-operation between law and order agencies, saying it has "never been better".
"That is particularly evident with the recent successes against those involved in human trafficking."
Mr Ford also noted achievements in seizing smuggled tobacco, counterfeit goods and illicit fuel.
Mr Ahern said while there is no point underestimating the threat posed by organised criminals, he said the authorities have made significant inroads in tackling the problem.
He told delegates: "I salute those successes and have no doubt all right-thinking people north and south join with me in doing so."