Gerry Adams and Martin McGuinness have urged the IRA to disarm in a bid to save the peace process.
In an eagerly anticipated speech to party activists in west Belfast, Mr Adams said the two Sinn Fein leaders had told the IRA in talks a decommissioning move would resolve the crisis facing the political institutions.
He confirmed: "Martin McGuinness and I have held discussions with the IRA and we have put to the IRA the view that if it could make a groundbreaking move on the arms issue that this could save the peace process from collapse and transform the situation."
However, the West Belfast MP said he did not underestimate the difficulties this presented to the IRA.
Mr Adams said he expected the enemies of Irish republicans to disparage any move by the IRA.
He also predicted other people would claim the IRA had acted under pressure.
But the Sinn Fein leader added: "Everyone else knows that the IRA is not an organisation that bows to pressure or which moves on British or unionist terms.
"IRA volunteers have a view of themselves and a vision of the Ireland they want to be a part of. This is what will shape their attitude to this issue.
"Republicans in Ireland and elsewhere will have to strategically think this issue through."
The Sinn Fein president said republicans were now entering a "good but challenging" period.
He urged them to remain focused on building peace and to do their utmost to prevent the situation from sliding back into conflict.
Mr Adams paid tribute to the IRA, claiming its members had been "at the heartbeat of the struggle for justice and freedom".
In an appeal for unity, the West Belfast MP continued: "In my view the IRA is genuinely committed to building a peace process in which the objectives of Irish republicanism can be argued and advanced.
"The Army has repeatedly demonstrated leadership and patience and vision and I respect absolutely its right to make its own decision on this issue.
"I would appeal to republicans to stay united.
"I would particularly appeal to IRA volunteers and their families and to the IRA support base, to stay together in comradeship.
"This is the time for commitment to the republican cause.
"It is a time for clear heads and brave hearts. The IRA must stand out as an example of a people's Army, in touch with the people, responsive to their needs and enjoying their genuine allegiance and support."
The Sinn Fein leader stressed the importance of other participants in the peace process responding positively to any gesture by the IRA.
"Generosity and vision on all sides can turn these current difficulties around and transform a crisis riven process into an organic and a people-centred movement towards a democratic peace settlement," he argued.
Mr Adams said he would not lecture unionists on their responsibilities but there was a collective need for them to settle their differences this time and he urged them to join with Sinn Fein in doing so.
He said he firmly believed republicans would have to "listen and learn" from unionists how they view their relationship with others on the island of Ireland.
As far as the British Government was concerned, he said, Prime Minister Tony Blair had to "right the wrongs and be part of building a new future".
"In fairness to Mr Blair, he has spent a great deal of time on the issue of Ireland but in my view this British Government has been too tactical in its approach.
"It has pandered too much to conservative elements within its own system and here in the north.
"It has not driven the process with the vigour and assertiveness that is required."Reuse content