Saturday, August 15, 1998 Published at 21:12 GMT 22:12 UK
Who are the 'Real IRA?'
Checkpoints were already being stepped up before the Omagh bomb
The finger of responsibility for the bomb attack in Omagh is being pointed at dissident republicans opposed to the peace process.
There are three main groups, each formed from splits in the movement over the last three decades.
The "Real IRA", which is blamed by many for this attack, is thought to operate from the Republic of Ireland.
The group is believed to have been responsible for a series of recent attacks, including a car bomb which devastated the market town of Banbridge, Co Armagh, earlier this month.
In May, following a mortar attack on a police station in Co Fermanagh, the "Real IRA" declared that it appointed an "army executive" and that a "war machine is once again being directed at the British Cabinet".
He lives in Dundalk, Co Louth, in the Irish Republic, and is thought to have taken with him a number of the IRA's bombmakers - as well as details of arms dumps.
This has increased the pressure on Sinn Fein to ensure that weapons are handed over before they get into the wrong hands, although the security forces insist that they do not believe the recent bombings have not been assisted by the IRA proper.
Reports put the membership of the "Real IRA" - also based largely in the Republic - at anything up to 100, and growing.
Bomb-making equipment had been seized and an apparent 'test' bomb blast was discovered when animals were startled and a crater discovered in farmland.
It is believed this was caused by a bomb of up to 1,000lbs set off by a paramilitary group hoping the sound would have been masked by a local fireworks display.
The INLA was formed in 1975, mainly from disaffected members of the IRA unhappy at a previous ceasefire.
It was responsible most recently for the murder of leading loyalist Billy Wright inside the Maze Prison on 27 December.
The security forces have linked it to attacks this year such as the Moira and Portadown bombs in February.
Action against the dissidents is now likely to be stepped up, concentrating on border areas, with more arms searches and surveillance of known sympathisers.
It has also been revealed by the security forces that a leading member of Sinn Fein from West Belfast had talks with the leader of the "Real IRA" and urged him to end the campaign.
The group's uncompromising stance was demonstrated by a senior RUC officer, who said: "The Sinn Fein representative was effectively told where to go."