There was no reason why Assembly elections could not be held next month, the Sinn Féin president said yesterday.
Mr Gerry Adams also claimed the IRA had delivered a "hugely advanced package" of intent to end paramilitary activity.
Speaking at a press conference in London, Mr Adams said Mr Tony Blair's decision to postpone the Stormont elections from May 29th to the autumn was a "slap in the face of the Good Friday agreement".
He rejected the British government's demand for more clarity from the IRA, saying it had made "very significant progress". The IRA released two statements on Tuesday night in which it insisted it was committed to making the peace process work and confirming it was poised to make a third act of decommissioning if agreement had been reached to restore the power-sharing Executive in Belfast.
But the Northern Secretary, Mr Paul Murphy, said the IRA statements were ambiguous and he demanded clarity. The Ulster Unionist leader, Mr David Trimble, accused it of playing word games.
Speaking at Westminster, Mr Adams said: "Mr Blair's decision to stop the elections is a serious mistake.
"It's as if the rulebook of conflict resolution has been torn up. Our view is that Mr Blair should reverse his decision on the elections. That he should enable them to go ahead as soon as possible. In fact there is no reason, and no credible excuse, why there cannot be elections in June." He said the joint declaration by the British and Irish governments was progress, although conditional and protracted.
"There are IRA statements and it is clear from them that there is an IRA leadership which is determined that there will be no activities that will undermine in any way the peace process and the Good Friday agreement.
"We have an IRA leadership that has stated clearly its willingness to proceed with the implementation of a process to put arms beyond use at the earliest opportunity.
"And very importantly, despite the suspension of the institutions, there is an IRA leadership which authorised the third act of putting arms beyond use.
"And also an IRA leadership which has stated publicly that if the two governments and all the parties fulfil their commitments, that it accepts that this will provide the basis for the complete and final closure of the conflict.
"All of us who are wedded to making this process work in considerable difficulties. Let me make it totally and absolutely clear, that Sinn Féin is in this process to the end.
"We are now, all of us, getting into a period of political uncertainty." Sinn Féin would campaign to have the elections held as soon as possible, Mr Adams said.
The current deadlock was due to the "refusal of elements within the British system, and particularly within unionism at this time, to embrace that change in a way that is positive".
"People have been cheated of their right to elections and entitlements and rights being upheld." Mr Adams added: "The reason I am saying the elections should go ahead is because Mr Blair or anyone else has no right to interfere with that process."
He refused to speculate on whether the IRA would release a further statement of intent, but added: "We have an IRA leadership that is determined that there be no activities which will undermine in any way the peace process and the Good Friday agreement."
Sinn Féin chief negotiator Mr Martin McGuinness said: "We are in this situation because effectively the British Prime Minister has caved in, not just to David Trimble, he has caved in to the rejectionist forces in the North."