Senator George Mitchell, Mr David Trimble and the Minister of State for Foreign Affairs, Ms Liz O'Donnell, in the face of considerable pessimism, have insisted that the Belfast Agreement can still be implemented.
Senator Mitchell, concluding the third week of his review, said there was no viable alternative to the accord and he accepted that the pro-agreement parties genuinely wanted to strike a deal.
Mr Trimble, the Ulster Unionist leader, said the agreement should not be written off. "You are far too soon to try to write its obituary. This process is a darn sight more robust than people give it credit for," he said.
"People know that this embodies the best chance they have had, or are likely to have, for decades. That is why it is far more robust, and that is why we will continue to do our utmost to ensure that the opportunities that are here are realised," said Mr Trimble.
"They have not yet been realised, but they are too big to turn your back on." Ms O'Donnell, who met Senator Mitchell and the Northern Secretary, Dr Mo Mowlam, at Castle Buildings, Stormont, said the parties must seize the opportunity for agreement.
"I am still convinced that, even though it won't be easy, there is a real chance of a breakthrough," she said.
Senator Mitchell, striking a similar note, said there was no alternative to the agreement. "I think all of the political leaders will have to recognise that this is the only credible way to move forward for this society," he said.
"I believe that this is the will of the decisive majority of the people and I believe there isn't any credible alternative that has been presented."
Senator Mitchell said he would take stock of how much progress had been achieved in the review within the next fortnight and then decide on the best way to proceed.
But he would not say how long he was prepared to remain as review facilitator, apart from stating that he could not participate in an "open-ended process" similar to the lengthy talks leading to the Belfast Agreement of April last year.
He said it would not be realistic to set a date for the end of the review at this stage. Such a judgment would be for later in the process, he said at Belfast Harbour Estate, where he officially opened a US company, Meridian Medical Technologies.
Equally, in the event of Sinn Fein and the UUP failing to reach a compromise, he had yet to decide whether he would present a take-it-or-leave-it formula for agreement to the parties.
"I have not made a decision on whether I will present a plan. I have not made a decision, if I do, what will be in it. I have not made a decision, if I do, when it will be. All of those things I am thinking about," he said.
He acknowledged there was considerable negativity about the overall political process, but he still believed the deadlock over the formation of an executive and decommissioning could be broken.
"I have had very extensive meetings with all of the pro-agreement parties. They are very serious. They want to try and get the job done. The difficulty is in translating that attitude and state of mind into concrete action," he said.
"I don't want to be unrealistic in a foolish way, but I would not be here if I were convinced that it could not be done. I'm still hopeful."
At Castle Buildings Senator Mitchell also met the DUP leader, the Rev Ian Paisley.
"We were telling him that he is redundant, that he should go home," said Dr Paisley. "We pointed out that he has an impossible task."
The Northern Ireland G7 group of business and trade union representatives said it was imperative that the difficulties were overcome. "Obviously, if it proves impossible to get devolved institutions, some alternative will have to be found, but it is highly unlikely that there is an alternative which will command more cross-community consensus than the Belfast Agreement or prove any easier to live with and to implement," the group said in a statement.
Senator Mitchell has flown to the US for the weekend and will return to Belfast on Monday. to continue his talks with the parties.
