The INLA, one of the deadliest and most ruthless paramilitary groups in the North, will announce tomorrow it has decommissioned its weapons.

Its political wing, the Irish Republican Socialist Party, will hold a press conference in Belfast city centre tomorrow morning, explaining the group's thinking. The INLA will also release a statement detailing it has put its weapons beyond use.

The organisation, which has held secret negotiations with the British, has also been involved in talks with the Independent International Commission on Decommissioning.

While the INLA's arsenal was not handed over to the IICD, international monitors witnessed its destruction. The INLA has long believed that the time is right "to leave the stage".

The decommissioning is expected to be welcomed by the British and Irish governments and Sinn Féin as a step in the right direction.

However, sources said the INLA will now expect its prisoners to be granted early release as were Provisional IRA inmates after the Good Friday agreement.

There is also speculation about possible funding for ex-prisoners' schemes. Three other republican organisations remain committed to armed struggle – the Real IRA, the Continuity IRA, and Real-IRA splinter group 'Óglaigh na hEireann'.

Sources said none of these groups planned ceasefires. A Real IRA source said that anyone who thought it would consider decommissioning or disbandment was "on another planet".

The organisation, which murdered two British soldiers at Massereene last year, remained committed to "challenging the occupation of our country until the British leave Ireland".

The INLA says that disbandment and decommissioning will allow the IRSP to grow. The paramilitary group has undergone an intensive internal debate on its future over the past year.

It has several hundred members on both sides of the border. It is strongest in Belfast, Dublin, Derry, Dundalk, Strabane, Galway and Waterford. It believes its membership will not join other republican organisations but dissident sources predict some defections.

In the late 1970s and '80s, the INLA rivalled the IRA for dominance. In 1979, it killed Airey Neave, Margaret Thatcher's close aide, in a House of Commons car bomb.

Three INLA prisoners died in the 1981 hunger-strike. But the INLA was later weakened by internal feuds. In 1997, the INLA murdered loyalist leader Billy Wright in the Maze.

Recently, the INLA has murdered several alleged drug-dealers in the north. Formed in 1974, with a mix of hardline republican and Marxist politics, the INLA's best known leader, Dominic McGlinchey, was murdered in 1994.