Twice in three years the group styling itself the "Real IRA" has tried to embarrass the Sinn Fein leadership at key points in the peace process.
In 1998 the Garda Special Branch intercepted a bomb of similar size to yesterday's on its way North three days before St Patrick's Day. The purpose then, as now, was to carry out a headline-grabbing attack which would undermine the Sinn Fein leaders.
At that time, the Sinn Fein leadership was close to accepting the terms of the Belfast Agreement, which would draw Sinn Fein into government in Northern Ireland for the first time. That Garda interception saved the day. The "Real IRA" then carried out attacks on vulnerable civilian targets in the North, culminating in the atrocity in Omagh in August 1998 in which one of its bombs killed 29 people and injured 300.
According to senior security sources on both sides of the Border recently, the same group was again planning a major attack to try to destabilise further the political process. The bomb intercepted by the RUC outside Belfast could have caused serious difficulties for the Sinn Fein leadership when it is already under pressure due to the collapse of the assembly.
A security alert was issued in the North as this week began, anticipating a bomb attack originating from the south Armagh Border area and aimed at a security target. The explosives were only a few miles away from the British army's Northern headquarters at Lisburn.
The "Real IRA" has attempted two attacks on the security forces in the North in the past month.
On February 25th, its members in Derry breached security at the British army's training camp at Ballykelly. Security around the base had been reduced since the ceasefires and the bombers cut through a chain-mesh fence and planted a bomb in two gas cylinders.
However, the bombers were disturbed and were unable to connect the cylinder packed with home-made explosive to the timer-power unit, which was abandoned around the corner.
The regimental sergeant major of the Royal Welsh Fusiliers, whose bedroom was at the end of the soldiers' dormitory, was roused by sounds of the intruders and it is believed they panicked when they heard him getting up and making for the door.
The power unit exploded harmlessly, showering broken glass over his bedroom. Had the bomb exploded, it would have caused multiple deaths.
Four days later, another attempt to kill members of the security forces failed when another "Real IRA" team was interrupted.
This unit was armed with an RPG-22 rocket launcher, the first of its kind found in Ireland. The discovery has alarmed security figures on both sides of the Border. The shoulder-launched rocket was made in Russia or Bulgaria in the mid-1990s and is one of the most powerful weapons of its kind.
According to information from the manufacturers, the RPG-22 is capable of piercing steel armour of up to 16 inches thick. It could also pierce a metre-thick concrete wall, which means it could breach any army or RUC base. The RUC in Co Tyrone discovered the rocket launcher after a local priest noticed men acting suspiciously in the parochial grounds in Killymeal Road, Dungannon on February 29th. When the police responded to the call the men fled, abandoning the rocket. A few days later cars in the parochial house were set on fire, it is believed by the dissident republicans.
According to security sources in the North, both of these attacks could have had fatal consequences. Both attacks were well prepared and the "Real IRA" has access to high-class terrorist equipment. In both cases its planning and surveillance were not noticed by the security forces.
However, sources say the "Real IRA" does not yet have people who are capable of carrying through such operations in the way its predecessor, the Provisional IRA, would have done.
Garda sources say the "Real IRA" has had success in recruiting young people in the Republic and Northern Ireland. They think it is a matter of time before the group succeeds in carrying out another fatal attack in Northern Ireland.
The group, based around Dundalk and south Armagh, broke away from the Provisional IRA in late 1997. Its leader is a former IRA quarter-master who had access to bomb-making equipment and some weapons. A woman from the Dundalk area is said to be one of its most hardline leading figures.
After the Omagh bomb several "Real IRA" members in Northern Ireland fled South, fearing retaliation. They held a meeting in the west of Ireland and then forced the leadership of the group in Dundalk to announce it was on ceasefire.
For a time the group was afraid of severe sanctions against its members, after both governments announced new anti-terrorist legislation following the Omagh bombing.
However, the group's leadership correctly assumed there would be no draconian response against it. This week the Garda Commissioner, Mr Pat Byrne, confirmed there was little scope for hoping that further charges would be brought over the Omagh bombing. His sentiments were endorsed by the RUC.
Garda intelligence sources found that within a few months of Omagh the group was reactivating and considering a new military campaign. It began recruiting and training new members in Border areas and nationalist areas of Belfast and Derry.
One of its leading members, from Co Monaghan is known to have travelled to the former Yugoslavia early last year.
It is believed he made contact with arms sources in either Belgrade or Croatia. The RPG-22 found in Dungannon and another, slightly less powerful RPG18 found in Co Meath last October are believed to have been shipped to the Republic through Croatia.
The "Real IRA" still has dozens rather than hundreds of members, according to Garda sources, but it may still attract support from former Provisional IRA members disillusioned with the continuing ceasefires.
However, senior security figures say the interception of the "Real IRA" attack and arrests should make it more difficult for the organisation to recruit and grow in the short term.