Image caption A sign in Lurgan's Kilwilkie estate threatening informers

There needs to be greater scrutiny of the relationship between MI5 agents and dissident republicans in Northern Ireland, a Sinn Féin minister has said.

John O'Dowd accused both dissident paramilitaries and some within the security services of being "conflict junkies".

He raised concerns that some informants may, in certain circumstances, be protected from prosecution.

Police acknowledge MI5 has informants working within dissident groups.

However, senior officers say the security service's role is only to gather information.

However, Mr O'Dowd said: "Twenty-five years ago, when people said there was collusion between the state and paramilitaries, they were accused of 'provo propoganda'.

"It is now clear that it was not propaganda and it cost people their lives.

"I think, now, there is a responsibility for us to challenge the security services to ensure their staff and their agents are not operating these organisations.

Image caption John O'Dowd has called for greater scrutiny of the relationship between MI5 and dissident republicans

"There is a common cause between conflict junkies, whether they be under the banner of republicanism or in MI5."

Police believe dissident republicans were responsible for a bomb attack in Lurgan earlier this month which, they said, was intended to kill.

Officers were lured into an area close to Mr O'Dowd's constituency office by reports of a suspicious object. As they were examining it, a second device exploded.

Assistant Chief Constable Will Kerr, head of the PSNI's crime operations department, said: "Intelligence is critical for every single facet of policing.

"But it is subject to such a heavily regulated statutory regime that the things that are alleged by some of those commentators simply could not happen and do not happen,"

ACC Kerr said he was concerned that phrases like "war junkies" and "conflict junkies" were being used by elected representatives.

"We need to be very careful about the language we use in Northern Ireland because what we do not want to do is to give these small unrepentant, unrepresentative groups a legitimacy or a justification for an attempt to kill local police officers," he said.

Image caption ACC Kerr said he was concerned at the use of terms like 'war junkies'

"You can never justify that."

This week, police searches in Londonderry focussed on what the police described as "dissident terrorist activity".

There are several different dissident republican groups, but their total membership is thought to be small.

However, there are areas where they have small pockets of support and there is a concern that some organisations may try to take advantage if Northern Ireland enters a period of political instability.

Both unionist and mainstream republican politicians have said that Stormont's future is in question because of rows over welfare reform, budgets and troubles-related issues.

"I would think that people involved in that would naturally want to exploit any kind of weakness that is appearing in the (political) set-up in the north of Ireland," said Cait Trainor who calls herself a dissident republican.

Ms Trainor made it clear that she is not involved with any violent or paramilitary groups, however she did not expressly condemn their recent actions.

"I do not think that trouble or bombs going off is a good thing - I would never sit here and say that," she said.

"But, ultimately, what I think is a worse thing is the ongoing occupation of Ireland."

All of Northern Ireland's main political parties and the police have repeatedly said that it is important to highlight the positive changes in Northern Ireland as a result of the peace process.

They have warned that support for dissident groups threatens that progress.