Mr Gerry Adams has said it is now up to the UUP to determine if it wants a successful outcome to the peace impasse.
The Sinn Fein president, in a reference to the UUP leader, Mr David Trimble, said that ultimately the success of the Mitchell review depended on political leadership.
"Success in this process requires that those in political leadership fulfil their responsibilities and give leadership," he told reporters at Castle Buildings, Stormont, yesterday after Senator George Mitchell adjourned the talks until Monday.
Mr Adams reiterated that the UUP had rejected the compromise deal on IRA disarmament and the formation of an executive fashioned during the discussions this week.
The weekend adjournment would "provide yet another opportunity for the unionists to consider where they want to go from here and whether they want this process to succeed", added Mr Adams.
"Sinn Fein have demonstrated that we want it to work. We have made strenuous efforts, taken initiatives, stretched ourselves and our constituency to the limit in a serious and genuine effort to resolve this crisis during this review," he said.
"We will be back on Monday to conclude the review. Hopefully the conclusion will be a positive one," Mr Adams said.
Senator Mitchell is understood to be travelling to London for the weekend and will return to Stormont on Monday. In a statement yesterday he said his review had reached "the final and most critical phase".
"Accordingly I have asked the parties to pause over the weekend and reflect on the magnitude of the decisions they have to take," he added.
"I recognise that this process has gone on much longer than originally intended. However, given the gravity of what is at stake, it is appropriate to take the time necessary to thoroughly and carefully consider these important matters. I ask all concerned for their patience and understanding," he said.
The SDLP deputy leader, Mr Seamus Mallon, said he was prepared to stake his reputation that no one other than Senator Mitchell could get closer to bridging the gap between Sinn Fein and the UUP on decommissioning and devolution.
The Ulster Unionist deputy leader, Mr John Taylor, has disclosed that he opposed the proposals aimed at breaking the deadlock over decommissioning and setting up the executive.
Speaking yesterday at Stormont, he said the proposals offered nothing new. "Sinn Fein are to a certain extent irrelevant because they say they are no longer connected to the IRA. The IRA are the relevant people," he said.
His party would continue to study the political situation. Considerable progress had been made over the past few years. "Both sides have moved but we must all move so we meet together on the path of democracy," he said.
He said this was not possible while the Provisional IRA retained its arsenal. A senior UUP negotiator, Sir Reg Empey, insisted the Mitchell review had not yet failed and his party would do its best to make it work.
He dismissed some media reports that the UUP Assembly group had rejected the proposed deal by a 14-13 vote as "totally mischievous with no basis in fact" but refused to specify exactly what took place.
The Ulster Democratic Party leader, Mr Gary McMichael, said he hoped the break in the Mitchell review would provide the opportunity for a successful conclusion. He said: "If this review ends without agreement it is very unclear what the next step would be."
The UK Unionist Party leader, Mr Bob McCartney, said the Mitchell review was brain-dead but its architects just did not have the courage "to switch the life support machine off".
The Northern Secretary, Mr Peter Mandelson, said the peace process was at a very critical stage but he believed the proposals on the table could satisfactorily deliver both devolution and decommissioning.
"Of course, we are on a knife-edge. I am not disputing that, but we are on a knife-edge with a lot going for us, too."