Sinn Féin has dismissed the unionist timetable and ultimatum as a "wreckers charter".
There is an electoral context to the decisions of the Ulster Unionist Council, the Sinn Féin president Mr Gerry Adams said, "but the reality is that the UUC decision is evidence that political unionism has not yet risen to the challenges presented by the imperative for change".
Mr Adams said his party would carefully consider the working of the unionist resolution and not engage in knee-jerk politics.
However, there was immediate and concentrated criticism of the tactics adopted and allegations of unionist intransigence in the face of the push for change.
"This cannot be tolerated, " he said. "I think it is very important that the two governments move to fill the vacuum that has developed. There is no alternative to the Good Friday agreement and to the process of change it requires."
Mr Adams reiterated Sinn Féin assertions that the British government was pandering to unionism in an attempt to keep it on board the political process. A senior Sinn Féin member told The Irish Times that Downing Street's "save Dave" campaign was to blame for much of the political turmoil.
Mr Adams said the ninth UUC meeting on the agreement also saw the ninth occasion on which the British government made concessions, "and it is the ninth time that the UUP has pocketed these concessions and made more demands".
What he called "the victory for the No camp" will not deter Sinn Féin "and will not stop the process of change", he vowed. "That will only happen if we give up and we are not giving up."
He denounced unionist demands as insatiable; they were coming on the part of people such as Mr Jeffrey Donaldson, "who have made it very clear that they are against this agreement".
"What we have to do is draw a line. We want the unionists to be part of that process, but maybe the unionists are just not up to it."