It is much more menacing than the two earlier rebel groupings, the Continuity IRA and the Irish National Liberation Army, which have been intermittently attempting to sabotage the peace process since it began with the first IRA ceasefire in 1994.
Both the latter were regarded as a containable fringe of extremists, but in recent months the Real IRA has mounted a substantial terrorist campaign - and has now been joined by the two smaller groups .
It was set up last October by the IRA's former Quartermaster-General, a man from Co Louth in the Irish Republic, who resigned in disgust after the second IRA ceasefire and took with him much of the IRA's bomb-making expertise and access to timing devices, detonators and substantial quantities of explosives. He has now been joined by perhaps 100 IRA activists who feel that the Good Friday peace agreement is a sell-out because it does not lead directly to a united Ireland.
The group is believed to have been responsible for a series of recent attacks, culminating in a 500lb car bomb which devastated the market town of Banbridge in Co Down.
Earlier in the month,a Real IRA bombing campaign in London is believed to have been foiled with a series of arrests, and several Real IRA car bombs destined for England or Northern Ireland are understood to have been intercepted by the Irish police so far this year.
In May, following a mortar attack on a police station in Co Fermanagh, the group declared that it had appointed an "army executive" and that a "war machine is once again being directed at the British Cabinet".
Two names were yesterday on the lips of everyone in Ireland discussing the republican dissident groups: Bernadette Sands and Michael McKevitt.
Ms Sands, sister of Bobby Sands, the IRA hunger striker who died in the Maze Prison in 1981, is an unflinching republican extremist who last year founded the 32-County Sovereignty Movement, regarded by the security forces on both sides of the border as the Real IRA's political face.
Michael McKevitt, a well-known republican shopkeeper from Dundalk, who was shot in both legs in 1975 in a feud with the Official IRA, is her partner.
According to Ms Sands-McKevitt, as she styles herself, she is purely and simply a spokesperson for a movement which she says has no associations with terrorism and is not even a political party, but rather a pressure group for Irish independence.
Ronnie Flanagan, Chief Constable of the Royal Ulster Constabulary, said some months ago that he believed the head of the Real IRA was aligned to the Sovereignty Movement, or Sovereignty Committee as it was then called.
He added: "People very close to that committee have a military capability, have an expertise and knowledge that we would assess has been deployed in recent attacks. There is a knowledge and expertise there that could be brought to bear in terrorist attacks."
Sinn Fein's national chairman Mitchel McLaughlin said last night that police on both sides of the border knew who were responsible. "We are talking here about a relatively small number of people who in all probability are guilty of what happened yesterday," he said.
He told BBC Radio Ulster: "The unfortunate reality is that there are those, possibly very young and inexperienced and idealistic people who are being affected by the rhetoric of these people who we don't know, who no one knows."
Earlier this year, Ms Sands-McKevitt conducted an newspaper interview in mourning clothes, having just attended the funeral of a Real IRA member who had been shot dead by Gardai during an armed robbery in Co Wicklow.
She commands instant attention in Ireland as the sister of Bobby Sands. The hunger-striker, who was elected to Westminster while in the Maze prison, remains one of the republican movement's most potent icons and martyrs and a large portrait of him, regularly re-painted, is the most prominent republican mural on the Falls Road in Belfast.
His sister's argument is essentially that he did not die, after a 66- day hunger strike, for the sort of agreement which Sinn Fein has just accepted: "I can't see what they are doing as being compatible with what Bobby died for," she said.
A mother of three children, she moved out of Belfast 20 years ago to Dundalk, where she runs a small business, and was largely unknown to the public until last year, when she stepped out from a background role to give regular media interviews.
In these she often forecasts that republican violence will continue, though her predictions are generally cast not in the form of threats but as statements of the inevitable.
She and her movement are implacable opponents of the peace process and the Good Friday agreement. She told one interviewer: "The whole thing is just a re-structuring of British rule in Ireland."
She told another: "Peace is not what our people fought for. They fought for independence."
Criticising Sinn Fein leaders Gerry Adams and Martin McGuinness, she declared: "False hope was generated by some people. The message sent out was that there was light at the end of the tunnel for republicans and, if we held hands, we would come through.
"But that wasn't true. I am firmly convinced we are being conned. I believe the talks are a farce. There are those prepared to compromise and that is totally wrong, totally wrong."Reuse content