Although the IRA has maintained a ceasefire since 1997, break-away republican paramilitaries still pose a major threat to a lasting peace settlement in Northern Ireland.
Extreme republican figures belonging to the Irish National Liberation Army, the Continuity IRA and the Real IRA plan to continue to fight against a political settlement which stops short of a united Ireland.
Reports of preparations for more violence is a major concern for the British government, which has banned the groups. But it is also a worry for the IRA and Sinn Fein leadership.
After the Omagh bombing Sinn Fein president Gerry Adams said violence "must" be a thing of the past. Senior IRA officials visited the homes of those thought related to the bombing to persuade them to close down.
Nevertheless at least three republican splinter groups are now active.
The most well-known splinter organisation is the Real IRA, which only emerged since the IRA ceasefire. The group claimed responsibility and subsequently apologised, for the Omagh bombing, which killed 29 people in August 1998. It was the worst atrocity of the Troubles. The organisation called a ceasefire a month later but it has not been recognised.
The Continuity IRA and INLA have been active for much longer. The Continuity IRA was established as the military wing of Republican Sinn Fein in 1986 but it is seen by many as disorganised and amateurish.
The INLA has existed as a small hard-core paramilitary group since the 1970s. It was responsible for the killing loyalist paramilitary leader Billy Wright in the Maze prison in January 1999 which sparked a spate of loyalist violence in which 12 Catholics were killed. Neither group has announced a ceasefire.