The dissident faction, believed to be some 50-strong and formed from units of the Provisionals opposed to the Good Friday peace agreement and the so-called Continuity Army Council, is said to have access to arms through a former IRA quartermaster.
News of its existence was made public yesterday in order to overshadow today's Sinn Fein conference at which mainstream republicans will vote to back the agreement in the referendum on 22 May. In a message, which was accompanied by a code word, the dissidents said that "a war machine is once again being directed against the British cabinet".
But Mo Mowlam, the Northern Ireland Secretary, commented later: "We will not be intimidated by them or anybody else.
"Any threat is worrying in Northern Ireland, and what I want to make clear is that our government is not going to respond to intimidation. We have a chance to build a different future. This will make the situation more complicated, but it mustn't deter us from where we have to go."
A Sinn Fein spokesman said: "Obviously any threat of armed action is worrying, but we do not believe that this group has the potential to do great damage."
However, there are parallels between the emergence of the dissident faction and the formation of the Provisional IRA from the Official IRA in the early Seventies.
Meanwhile, the Chancellor, Gordon Brown, will this week announce a regeneration and investment package for Northern Ireland valued "in the high tens of millions", plus two major inward- investment projects by the private sector.
He will also visit the province, the first Chancellor to do so for decades.
Mr Brown said yesterday: "This package will be a major boost for Northern Ireland's economy. The Good Friday agreement should be seen as a catalyst for change."
Elsewhere, 300 people turned up to stand in the rain in Moygashel and hear the Rev Ian Paisley say no, no, and no again to the Northern Ireland peace process, and condemn its backers as agents of the Devil.
Peace hopes are expected to face their most serious threat with the coming loyalist marching season. Dr Paisley declared: "Some of us here will be back up Drumcree and back again ... it's no, it's no, and it's no surrender."Reuse content