Who are the dissidents?

Real IRA

The Real IRA was born out of a split in the mainstream Provisional IRA (PIRA) in October 1997, when the PIRA's so-called quartermaster-general resigned over Sinn Fein's embrace of the peace process.

Shortly after its formation, the paramilitary group quickly took over from the older Continuity IRA as the leading home for dissidents.

However, the security forces believe the two organisations have co-operated in a number of attacks.

The Real IRA was responsible for the Omagh bombing in August 1998. It was also behind a string of subsequent attacks including the car bombing of BBC Television Centre in west London in June 2001 and the shooting of two soldiers at Massereene army base earlier this year.

According to the Independent Monitoring Commission (IMC), the Real IRA and Continuity IRA are increasingly working more closely together to increase the threat posed to security forces.

The Real IRA is thought to be split into two fairly distinct factions, each with its own leadership structures.

Continuity IRA

The Continuity IRA (CIRA) has its origins in a split in the IRA which centred around opposition to republican candidates taking seats in the Irish Republic's parliament.

In 1986 some members of Sinn Fein, angry at the party's decision to end its policy of abstention broke away and formed a new party called Republican Sinn Fein.

The security forces say the CIRA was set up as the military wing of Republican Sinn Fein, although the party says that is not the case.

For many year the CIRA was a very small and largely inactive group. It announced its reappearance in 1996 when it destroyed a hotel in County Fermanagh with a bomb thought to contain more than 1,200lbs of explosives.

It is believed most of its members are concentrated in Counties Fermanagh and Armagh.

It claimed responsibility for the murder of police officer Stephen Carroll in March 2009.

Irish National Liberation Army

The Irish National Liberation Army was formed in 1975, mainly from disaffected members of the IRA unhappy at a previous ceasefire. It has killed more than 150 people.

Its most high profile murder was that of Loyalist Volunteer Force leader Billy Wright, who was shot dead in the Maze prison in 1997.

The INLA regularly indulged in bouts of bloody infighting and became involved in organised crime, such as extortion and robbery.

It claimed responsibility for the murder of a drug dealer in Londonderry in February, but was considered to be the least active of the dissident groups in recent years.

On 11 October 2009, the INLA announced that its armed struggle was over and said its objective of a "32-county socialist republic" would be best achieved through exclusively peaceful means.

Oglaigh na hEireann

The name Oglaigh na hEireann (which roughly translates as soldiers of Ireland) has been used by a variety of groups.

A group operating under the title split from the Continuity IRA in 2006.

More recently it has been used by a faction of the Real IRA.

It is said to include some of the most experienced terrorists from the Provisional IRA.

The IMC reported in November 2008 that the group "continues to pose a serious threat, both as a paramilitary group capable of extreme violence and because of the criminal activities of its members."

That assessment followed an armed robbery in March 2008 which was carried out in the Strabane area by an Oglaigh na hEireann member.

In August 2008, suspect items were found in searches in Fermanagh, which were also associated with Oglaigh na hEireann.

However, little activity has been reported by the group since then.

Coincidentally, Oglaigh na hEireann is also the official Irish-language title for the Irish defence forces.

Irish Republican Liberation Army

The IMC has assessed the Irish Republican Liberation Army as "essentially a group of criminals taking a republican banner in order to give supposed status to their activities".