The bulk of the South Derry brigade of the Provisional IRA has broken away from the organisation because of its disillusionment with the leadership, republican sources have told the Sunday Tribune.
It's the most serious division in republican ranks since the split which led to the formation of the Real IRA in 1997.
Sources close to the men who left said they were committed to the 'tactical use of armed struggle' and planned to carry out intermittent attacks on the security forces.
They said the men did not want to join either the Real or Continuity IRA but would collaborate with both groups. It is understood they also want to hold discussions with the INLA.
"They don't want to amalgamate with any other organisation but they want to work with other republicans and build an anti-Good Friday Agreement front," the source said.
The source claimed the men were "completely disillusioned" with the stance of the Sinn Féin and IRA leadership on a range of issues, but particularly on policing.
The 25 men, compromising almost the entire brigade, resigned from the Provisionals within recent weeks. The source alleged the men had weapons but would not disclose any details. He said the defectors included seasoned activists in their 30s and 40s, and men in their 20s who joined the IRA after the ceasefire.
Another source close to the men accused the Adams-McGuinness leadership of abandoning the last vestige of traditional republicanism by wanting to sign up to support the Police Service of Northern Ireland.
The brigade saw this as "yet another ideological u-turn". They had grown increasingly unhappy with various political compromises and policy shifts over the years, he said.
Last year, around 20 IRA members resigned in north Belfast amidst disillusionment with the leadership but they walked away from all military and political involvement.
The biggest threat to the peace process occurred in 1997, when senior IRA members, led by the quarter-master general, Mickey McKevitt, resigned from the Provisionals and formed the Real IRA.
They were supported by units in the Republic and the bulk of the IRA's First Battalion in South Armagh. The Real IRA went on to carry out an armed campaign, bombing commercial and security targets across the North and in Britain.
In recent years, the intelligence services have had remarkable success against dissident republicans through high-tech surveillance and informers.
While the security forces will be concerned about the latest developments, the threat from the South Derry men is substantially less than that following the 1997 split.
The latest dissidents will be operating within a limited geographical area. Earlier this month, a nail bomb, complete with command wire, was found in Bellaghy, Co Derry. The police said the device could have "caused death or serious injury" and described it as a "sinister" development.