The Sinn Féin president, Mr Gerry Adams, has warned that unionists and the two governments ``have set the bar too high'' for republicans.
Demands were being made of republicans, he said, while the British and Irish governments were in breach of the agreement.
He said that the political process would be in deep trouble if a way out of the impasse was not found.
Mr Adams was speaking following his latest meeting with Ulster Unionist leader David Trimble.
Parties are currently involved in a hectic round of meetings at a critical stage in efforts to secure the return of power-sharing institutions in the North and the full implementation of the 1998 Good Friday Agreement.
Bilateral talks involving the British and Irish governments and the parties are expected in Belfast, London and Dublin this week.
The negotiations appear to have hit a serious snag with the effective rejection on Friday by the UUP of the Joint Declaration, the plan drawn up by the two governments earlier this year for the implementation of the Good Friday Agreement.
There is increasing speculation that the overdue Assembly elections could be called without a new deal for power-sharing in place, but would be followed by a formal Review of the Good Friday Agreement.
The preferred date for an election remains Thursday, November 13th, which means it must be called by next week, to allow the electoral office prepare for the poll.
Mr Adams cautioned that putting off the twice-cancelled Assembly election would be to wave goodbye to this phase of the process.
``My big concern at the moment is that the two governments and the Ulster Unionist Party have set the bar too high... right outside the agreement,'' Mr Adams said.
Mr Adams said the UUP, as a result of its executive resolution on the joint declaration, meant that the rejectionists and other wings of the party had joined to move backwards and away from elements such as the Human Rights Commission, the Equality Commission, justice issues and other matters at the core of the agreement.
He complained that there was not a commitment to sustained institutions.
``We need to have our heads around just how difficult the process is at this time. We continue to work at it,'' Mr Adams said.
Asked whether he believed he could make progress with Mr Trimble over the next few days, he replied: ``We all are subject to this business of going down to the wire.
``The Sinn Fein case has been transparent. We have said from the beginning that we are prepared to play our part and we are prepared to stretch beyond ourselves and beyond our commitments under the agreement but we cannot do any of that in the absence of a date certain, publicly promulgated, for an election.''
Mr Adams said the process could still be delivered but there was only so much one party could do on its own.
``There are just so many difficulties being raised,'' he said. ``Last Friday the rejectionist unionists had their way.
``I look at the Ulster Unionist resolution and read through it and see rejection of element after element after element of the Good Friday Agreement.
``I then read demands... but the UUP wants to see the IRA going away and Sinn Fein's peace strategy is to achieve that objective. At the same time as they want that to happen they are against the British army going away and they want to see the RIR retained. It just doesn't make sense.
``How do nationalists read that? Unionists want the IRA to disappear on the one hand but they want a small, locally recruited militia to be maintained and they want the British army to stay in Crossmaglen, in Carrickmore or wherever else it is throughout the six counties. This is madness.''
However, Mr Trimble blamed republicans, accusing the IRA of failing to decommission completely within two years and disband.
Mark Durkan, leader of the rival nationalist SDLP, said he was confident that there would be an assembly election.
Speaking before his meeting with the British Prime Minister in London today, he said: ``I think the Prime Minister will feel that even in the absence of a deal or a clear cut position there is going to be no grounds for further postponing an election.''
However, the Irish Prime Minister warned of a ``total mess'' if agreement among the Northern parties and the Irish and British governments is not finalised.
Bertie Ahern told the Irish parliament in Dublin yesterday: ``We have not as yet got to a position where we have the basis of an agreement where we can say that we can move into elections positively.
``The difficulty is if we don't approve this in the next period of time we could get into an election situation that would just lead to no progress and everybody fighting the elections on a negative position.''
Meanwhile, United States President George W Bush's special envoy to the Six Counties Richard Haass, will travel to the North next week as efforts to revive devolution intensify. It is expected that Mr Haass will hold a round of meetings with the various parties on October 13-14.