The Irish National Liberation Army (INLA), one of the most lethal paramilitary groups in the Northern Ireland conflict, will announce on Sunday its intention to disband, Irish media reported.
A leader of the INLA's political wing the Irish Republican Socialist Party will make a statement later on Sunday in Bray, south of Dublin, at a commemoration for Seamus Costello, the party's founder, newspapers and radio reported.
Fighting between pro-British and Irish nationalist groups killed 3,600 people before a 1998 peace deal that was followed by pledges by the main militant organisations on both sides including the Irish Republican Army (IRA) to disarm.
Sporadic violence still occurs however and the killings of two British soldiers and a policeman in March by Republican splinter groups opposed to the peace process threatened to further destabilise Northern Ireland.
U.S. Secretary of State Hillary Clinton is due to hold talks in Dublin on Sunday and in Belfast on Monday about the situation in Northern Ireland.
Underlining the continuing security threat in the UK province, ten police officers were wounded in a "serious disturbance" involving 150 people in the county of Armagh south of Belfast in the early hours of Sunday, police said.
It said none of the injuries were believed to be serious.
Politically to the left of the IRA, the INLA broke away in 1975 and became one of the most ruthless Republican guerrilla groups killing British politician Airey Neave in a 1979 bomb attack in London.
The group, which had a history of violent in-fighting, called a ceasefire in 1998, but an independent report in 2007 said that while activity was at a low level it remained a threat due to its involvement in serious crimes.
Ireland's national broadcaster RTE said the INLA would announce on Sunday its "war was over" and some reports said it was expected to disarm within months.
The Sunday Tribune newspaper, which has good connections to dissident groups, said the paramilitaries will not announce the decommissioning of weapons and that future moves to disarm could involve demands to release INLA prisoners.
The INLA, like most other dissident groups, has been linked to criminal activities such as smuggling and drug dealing, and it has used bases in both Northern Ireland and the Republic of Ireland, especially around Dublin.
The Tribune said the Real IRA, which killed the two soldiers at a Northern Irish army barracks in March, had no intention of calling a ceasefire or disbanding.
"We are strengthening our ranks," it quoted an unnamed source as saying on behalf of the Real IRA.