Sinn Fein's Martin McGuinness is to demand a crisis summit with his co-leader in the Northern Ireland Assembly Peter Robinson in a attempt to save the power-sharing executive.
Republicans have accused the Democratic Unionist Party of doggedly refusing to make the Stormont parliament work as the fall-out deepens over the devolution of policing and justice powers.
Sinn Fein president Gerry Adams warned that if agreement can not be reached then the institutions set up under the Good Friday Agreement can no longer continue.
"This is not about Sinn Fein hyping things up," he said.
"This is not a game of poker. If the institutions are not working, if they are not delivering, then they become pointless and unsustainable."
Speaking outside a meeting of Sinn Fein's Ard Chomhairle, or ruling executive, Mr Adams insisted the talks between First Minister Mr Robinson and Deputy First Minister Mr McGuinness would be pivotal. "This will be a critical and defining engagement," he said.
In a clear warning that Sinn Fein was prepared to collapse Stormont, Mr Adams signalled his party would walk away unless outstanding sections of the Good Friday Agreement and St Andrews Agreement are implemented.
"If that is not possible, then no self-respecting public representative or political party would want to be part of nothing less than a charade," he said.
Mr McGuinness spoke with Prime Minister Gordon Brown and a senior official in Taoiseach Brian Cowen's department on Friday night as fears mounted over the future of devolution in Northern Ireland.
Mr Adams stated both governments were guarantors to the agreements, not referees, and demanded they set down a date for policing and justice powers to be handed over from London.
