The terrorist organisation — which was responsible for about half of the 3,000 deaths in three decades of the Troubles — will also announce that it will decommission all its weaponry over a set period.

Prospects of a breakthrough in the peace process will be tempered by unionist scepticism over previous initiatives by the Provisionals, which turned out to be false dawns.

But doubts about the importance of the imminent announcement were swept away by Bertie Ahern, the Irish Prime Minister, who declared that Ireland was days away from a ground-breaking move.

“I think hopefully, hopefully, because I can’t be certain on this issue, because I don’t control the writing of these statements, but . . . I do genuinely believe that we are within days of seeing an enormous change in the situation,” he said.

The announcement is expected this morning, but there was speculation that it might have come last night or be delayed until tomorrow as republican sources disclosed that the IRA wants to maximise its impact and not be overshadowed by the terrorist crisis in London.

In a clear indication that the choreography leading up to the statement had commenced, Sean Kelly, the Shankill Road bomber who was convicted of murdering nine people in 1993, was released from prison last night.

Mr Kelly, was sent back to prison last month for breaching the conditions of his release — something which he disputed.

The decision was seen as highly controversial in Belfast as it apparently breached legal procedures by leapfrogging the Sentence Review Commission which oversees all such cases.

Martin McGuinness, Sinn Fein’s chief negotiator, who has quit the Provos’ seven-member “army council” with Gerry Adams — was in Washington last night preparing to brief senior US government officials.

Peter King, the Republican Party congressman and a long-time Sinn Fein ally, said:

“Tomorrow should be a real turning point in Irish history.”

The announcement will come four months after Mr Adams, the Sinn Fein president, launched his party’s election campaign with a “personal appeal”, made before reporters, in which he asked the IRA if it believed that there was a political alternative to armed struggle. It is seven years since Sinn Fein signed the Good Friday Agreement.

The Provisionals will not announce their disbandment, a requirement dropped by London and Dublin during recent negotiations with Mr Adams but still demanded on the unionist side.

Mr Ahern emphasised that the terrorist group had to address all issues from arms to training and targeting.

“I have given you, I think, the issues that we want to see fully dealt with. We want to see the full range of arms and explosives and all of the military arms dealt with,” he said.

“We want to see criminality and . . . the targeting, the procurement, the training, all these issues fully and completely ended. The only way that can be done is if the Provisional IRA instruct their volunteers to end the campaign.”

In London, ministers firmly expect there to be a statement that the armed struggle has been abandoned. They hope that this will mean the IRA has ended activities such as crime, intelligence-gathering and targeting. But Tony Blair, who is poised to make a Downing Street statement today if the statement comes, will make plain that the Independent Monitoring Commission will be asked for a swift verdict on whether the IRA has ceased the behaviour to which both the British and Irish Governments have objected.

The IRA’s expected promise to destroy weapons is likely to be accompanied by a timetable fixed by John de Chastelain’s decommissioning body.

Senior government sources appeared to be optimistic last night that a breakthrough was imminent. One suggested that the statement would show that the IRA was “out of business as an aggressive force”.

Another said that the statement was the “biggie” that had been awaited for years. But ministers added that the yexpected unionists to react with caution.

“This will be a unilateral statement. Everyone will want to look at it and what follows from it before Sinn Fein is back in the government of Northern Ireland and the Assembly is reinstated,” one said.

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